Any general framework for deciding whether a story should be produced as a novel or screenplay? It seems a screenplay, while ideal for dialogue-rich stories, would regardless still be more sought-after commercially than a paperback
The people that invest the millions of dollars needed to produce a motion picture have a strong preference for established IP -- stories that already have proven audiences.
If you have no track record that supports that you've created a story that will be popular and profitable, then it is less likely you'll attract the interest of filmmakers. It's not impossible, just less likely.
If your story can be told in either prose or cinematically forms, then writing a novel is a good way to start.
But if your story relies predominantly on sudden visual elements: Prat falls, spit takes, massive explosions, outer space, undersea, or aerial dogfights, car or chariot chases, jump scares, etc., then more than likely it is easier to develop as a screen play.
I think you've got it wrong. Dialogue is actually sparse in a screenplay, what is preferred is visual stories that require little supporting dialogue.
In screenplay writing advice, it is consistently preferred if information can be conveyed in a visual manner, emotional reactions, action.
Indiana Jones says nothing peering into a cave, with his torch he sees thousands of rats, he reacts with disgust.
INDIANA Rats! I hate rats!
He steps into the cave, hating every second, grimacing, pushing rats away with his feet as he traverses the corridor, startling when a rat drops on his shoulder.
That may be inaccurate from memory, but the point being, you get a minute of screen time with 4 words of dialogue. He doesn't have to say rats creep him out, we get no words on the screen to that effect, all of this is visual, even comic.
Screenplays rely on visuals far more than dialogue.
That is how to decide. If your story can be translated into primarily a visual experience, then it may be a good candidate for a screenplay. That means virtually zero exposition or explanation about your world or what is going on. Conversations and solo speech more than 25 words or so is frowned upon, and under 10 words for a line is preferred.
You can see this on TV, notice how sparse speech is. How much is left out. How the actors "just get it" when somebody says something a little cryptic.
If your story requires a lot of soliloquies, conversations and exposition, it belongs in a novel. That is true even for the narrator, if they are explaining stuff instead of just describing the setting. Explaining stuff in Supers (text on the screen, a la Star Wars opening) is frowned upon in screenplays.
You need to tell an audiovisual story, sight and hearing. An emotional story, supported by music (composed, not by you, to support the emotions of your scene, which should be made apparent by you).
Thought pieces don't tend to work well on the screen. They want stories that are visually engaging and depend heavily on acting skills, great settings, etc.