I think you insult people who read books in the 1800s. They followed science fiction just fine, in fact it was everywhere. Folksy Mark Twain even wrote a story about time travel.
But let's go back to the OG:
Frankenstein; or, The Modern Prometheus by Mary Shelley (1818).
She does not explain how the creature is made. In the 1831 edition she removed some of the science that had already started to sound dated. In the book she only says that Victor has an epiphany, then studies anatomy (human corpses and living animals), and then creates life from lifeless matter. Victor very specifically calls his nameless creature 'a new species' and imagines how it will praise him as its creator. At the height of his hubris he imagines that someday, but not yet, he might be able to reverse death.
The extremely obvious theme of the novel is that Victor has god-like creative ability, but is an immature human being and a crappy 'father' (tip 'o the hat to every man she was hanging out with that summer in Geneva). Victor literally runs away from his responsibility, too horrified to nurture his creation.
Shelley at age 19, writes a book that is a lot of things at once – it is compassionate to the creature (who is a super-genius that debates philosophy with it's creator), she is on-the-nose critical of the men in her circle (Lord Byron impregnated her sister and refused to legitimize the child), and she shakes an angry teenage fist at god, asking: "What if God is just another immature fornicating cad who abandoned his offspring...?" There is also implied class criticism that Victor is a brilliant but amoral aristocrat, meanwhile the creature learns about family and love (and how to speak French) by spying on low-class peasants.
Hence, the subtitle about 'Modern Prometheus' – except in Shelley's novel Victor isn't punished by Zeus, it's the Creature that wants Victor to suffer. After denying it a mate, the creature kills Victor's fiance and chases him to the ends of the Earth (the North Pole). The creature is stronger, just as intelligent, and far more ruthless. Victor's only option is to head to a remote place and hope it dies there with him.
Most people won't read the book
By the time Mary Shelley returned to England, her angry-teenager-shakes-fist-at-god novel had been dramatized into (multiple) sensational plays where her creature becomes increasingly unrecognizable, no doubt playing up to the tastes of the audience who paid for a monster on a rampage.
Simultaneously, 'body snatching' was fueling media hysteria. Cadavers were needed to educate doctors creating a lucrative black market in fresh corpses. London papers routinely described barrels filled with cut-up bodies tumbling out of wagons. People started buying iron cages to protect graves. The trial of Burke and Hare changed modern horror from ghosts in castles to psychopath murderers who live next door.
In a very short time, the (unauthorized) plays morphed Victor Frankenstein into Burke and Hare. He's no longer a brilliant cad, he's a grave robber. The creature no longer debates philosophy, he is a imbecile bag of stitched up corpses that says "Grrr, Fire!". This is clearly not the same story, and runs contrary to the original theme. In the original story god is absent, personified by Victor being a negligent creator of a sympathetic angry new life. In the new story God's most sacred creation (man) is re-animated into a shambling monster – Victor isn't a god/creator, he is a pretender who just re-assembles God's creation, badly.... That whole subtitle doesn't even make sense now.
Shelley's original text supports both versions, sort of.
Ok, here's the weird part. Shelley's original text is worded vaguely enough to support the new version of the story – if you ignore the novel's subtitle and theme and every description of the creature.
The actual chapter where Victor makes the creature is about Victor's mental state, his mania of creation and eagerness to be praised for it. Her prose is densely purple, dropping mentions of human bones and visits to crypts to study anatomy – the sentences are mixed up like a feverdream, probably going for a dichotomy effect of macabre imagery interspersed with Victor's hubris, A.K.A. foreshadowing. Shelley paints skulls all over Victor's "I am gonna be so great" speech.
But when you read it, if you don't read too closely (which isn't hard to misread with the purple prose), and you already have this image of stitched-up corpses after a couple of centuries of the creature being presented that way, it's possible to interpret the text as exactly that. Shelley's 'bones and graves' symbology can be literally interpreted as: "Went to grave and got some body parts..., yadda yadda..., made a monster." It's not wrong..., but that's not what the creature is in the context of the rest of the novel.
The original creature is something from science fiction, he is an abstract: new life from nothing. Victor does become a god, just a very poor one, and is unprepared for the consequences of his own science-gone-amok – a classic sci-fi moral.
The new creature is a horror tour-de-force. What is scarier than human corpses coming to life, except a bunch of human corpses sewn together that come back to life with a murderer's brain – that is not science, it's the slam-dunk touchdown of all monsters. You could just keep going with strangler's hands, and peeping tom's eyeballs, lawyer's tongue, etc. Everything bad in one patchwork monster.
The new version is not a bad story – arguably more commercial in that more people know it, and it's the version that has survived in pop culture for 200 years. It's not the intended story, the novel that Mary Shelley wrote. It's 'dumbed down' and more sensational, like every Star Trek movie. There's a letter Shelley wrote after seeing one of the plays where she seems amused at how her character has drifted but also become a crowd-pleaser (she's not specific, and I haven't been able to find scripts of these early unauthorized productions, they seem to have been written by the companies that performed them).
To explain or not to explain?
Mary Shelley decided to not explain the science, which did not pretend to be speculative. She had seen demonstrations of 'spontaneous life' and electrical muscle stimulation, but she removed most of the science in her later edition. This was a choice.
Instead she wrote a hell of a story that swaps the Awesome Guy™ protagonist into unwilling villain, and the monster into all of us who are angry at the failures of society... and religion... and our parents.... It will forever be an outsider, teen-shakes-fist-at-god, get revenge on the Man, macabre-punk novel. That's timeless.
But..., the story that everyone knows is not what she wrote – and I don't think it's because she left out the specifics that everyone gets it wrong – the media portrayals just erase the author. It doesn't matter if she wrote the creature was made from clocks and pudding, if the movie shows stitched-up corpses that's what people know.
The problem is that her theme has changed. A defiantly atheist/socialist take that god does not deserve our praise/Everyone has rights at birth, becomes only God can create true life (that isn't a shambling abomination made from leftover scraps that says "Grrr" and fears fire... which also works against the Prometheus subtitle). These thematic differences are not at all compatible, they change the entire meaning of the story.
If she had been more specific about the 'science', I think the story would not have become something else entirely in the popular culture (my speculation, obviously I can't prove it). It is interesting to read Chapter 3 out-of-context and see how too much macabre symbolism and not enough science explanation is easily mis-interpretted as to what is even going on in the scene. I'm convinced the 'new' monster was also created by Shelley, but unintentionally (like Victor). If that's the only chapter you read, it's easy to get the impression the monster was directly assembled from human corpses. Later chapters do not describe a creature made from dead bodies, it is something new and unnatural, beautiful and revolting.
Write what you want and get the emotions right. Any science you are too specific about will be out-dated in a decade. When the movie comes out, Hollywood will destroy your intent anyway.