My recollection is that when I started reading romance novels in the 1980s, the majority (perhaps 60%) were written in the third person. This included some "young adult" romances with characters in their early 20s.
I stopped reading them until recently. "Nowadays," it seems that the vast majority of young adult romances (80%-plus) are written in the first person.
Why might that be the case for young adult romances, and is it "less true" for stories of "older" people?
In general teenagers tend to be (a) a little narcissistic and (b) intensely interested in their peers and what they think and feel. When you write in the first person as a teen protagonist, you are effectively taking on the persona and presentation of a peer, a fellow teen with whom they can empathize, rather than that of the distanced, adult, third-person narrator.
I'm actually currently in the midst of converting my own YA manuscript from close third person to first person. In addition to the above reason, I wanted to be able to present the worldview of my protagonist, with its prejudices and foibles intact, without the implicit endorsement of an authorial voice. There are also things that feel intrusive to report second-hand that you can report in a less filtered manner with a first-person narrator.
I'd be lying if I said that it wasn't also true that I noticed that almost all popular contemporary YA is in first person now (and we know how "on trend" teens like to be, even if they think of themselves as rebels). But the change also seems to have freshened and opened up the narrative. The biggest challenge, of course, is maintaining an authentic voice, in the face of not having actually been that age in a very long time.
Young adult generally is written in first person for the strong voice and the closeness of the POV. It has almost become industry standard, likely because it sells well for the target market. You can read articles and blogs expounding on the virtues of the viewpoint for the age. My guess is that, for the precise reason that it is monopolistically popular, we'll see another shift eventually, even if it's just rebeliousness.
The generic argument is that the POV is the quickest way to sympathetic feelings and investment. The strong voice let's the reader feel like they really know the character in a time when most Americans say they have zero close friends. And first person tends to sound more protag-y when done right, which moves the story along at a decent pace.
I doubt it is specific to romance. It seems to be everywhere. I keep finding books that have no reason to be in first person (and in some cases every reason not to be) which are in first person nonetheless.
In part it may just be a fad. It's a bit like the way people wore blue jeans when I was growing up. They did it to be different. All of them. I wanna be a rebel, as long as everyone else is being the exact same type of rebel too.
A deeper reason may be a societal lack of confidence in objective truth. The artist was traditionally supposed to be the truth teller. But today everyone has their own truth. Speak your own truth. Tell your own story. Third person narration is an assertion of objectivity. First person is an expression of personal truth. Or personal truthiness at least.
It may well be that young adults are particularly devoted to this entirely personal notion of truth, to truth being what you feel, not what you see. But it seems to be a fairly general phenomena. Art that does not lead the bandwagon inevitably follows it.
Teenagers are at a developmental stage where they must form an identity. They look at themselves, at the changes they go through, both physically, emotionally, and intellectually, and then they look at the world and wonder how they fit it, what their place is in society, and what they want to do about all that they see.
While adults have generally found their place and look on themselves and at life from the self-reflective vantage point of what in literature is best exemplified by a third person narrator, teenagers stare at themselves from their own disoriented excitement, and this emotionally wrought immersion in oneself is best portrayed through a very close first person almost stream-of-consiousness-like narrative.
I think the trend is a fad, like slang, like teens finding their own "language" to communicate (as every generation does), like fashion. Remember bell-bottoms? Like music. Remember disco?
Something sells, others emulate it, a fad emerges, only to be rejected when those that embrace it become "The Establishment", cops and politicians and parents and people with jobs -- So new teens that are biologically driven to separate themselves from their parents (to begin mating and having their own families) reject the old fad and start up their own.
A tiny part of that big dynamic is in what they like to read for fiction. Wait a generation. When these teens are parents, the books they loved will be too out of touch with their technology, fashion, and social norms, and new books will be needed, and they will likely be written differently by new norms.
I don't think there is a deeper meaning than that; just like I don't think there was a deeper meaning to bell-bottom jeans or disco. They were embraced not for any greater utility or being "better" on any rational scale, they were embraced for one crucial reason: they were different. Not your dad's straight-leg jeans, not your dad's music, not your dad's politics.
We're going to rebel against conformity! (But all in the same exact way as our peers, of course, we don't want to be that weird.)
There are a number of reasons. Some are universal, some are recent.
First person works best when you have only a single viewpoint character. YA tends towards smaller casts and simpler structures, which means that YA novels are more likely to have single viewpoints, and means that a higher percentage of novels have an opportunity for first person narratives.
(My finger isn't too closely on the pulse of YA since I outgrew the genre, but I haven't really heard of anything taking their place yet)
The glut of YA dystopian novels tends to attract disparaging remarks about "aping better novels", but there are reasons that trends get followed, particularly in YA. Young readers are still learning what they like, and will frequently turn to the book most similar to the one they just fell in love with. They aren't looking for "new and different" yet, because to them everything is new and different. So when a YA novel skyrockets up the charts then similar books get published hoping to pick up on the rebound.
At the moment, the most popular books have strong first person narrators. So other authors are looking to produce similar voices that the kids who loved the popular voices will hopefully love theirs as well.
Paranormal Romance is not entirely YA, of course, but with Twilight as the centerpiece there is a strong connection between them. And Paranormal Romance is largely an offshoot (or at least closely tied to) Urban Fantasy, which in turn draws a lot of its tropes from Noir. One of those tropes is a hard-bitten, snarky first-person perspective. Even when the viewpoint character isn't a detective (Once again I'm looking at you, Twilight), the tendencies of the genre are going to influence the decisions that authors make, consciously or unconsciously.
