I think it's more often angst at being forced to do the dishes.
Most things you see a lot in fan-fiction are, purely and simply, the result of writers copying each other. People like me who mock it for a hobby– we call ourselves "sporkers", and it's practically a subculture– know that there are a few basic elements that recur with absurd frequency in story after story, e.g.
There is a tenth member of the Fellowship.
Boromir is an evil misogynist.
The main character is Elrond's other daughter.
Or Sauron's daughter.
Legolas and Aragorn are boyhood friends and have adventures together.
Thranduil is a drunk and beats Legolas.
Either Legolas or Aragorn is blind/deaf/mute/crippled/scarred.
A male character has a baby. (AKA "Mpreg".)
Elladan and Elrohir are pranksters (a la the Weasley twins).
And, of course,
Abused girl is hit by a car, wakes up in Middle-earth and finds out that she is the Chosen One.
We actually classify fan-fics by their dominant cliches: "Look, another Blind!Aragorn".
What I'm saying is, there's no way fan-fic authors could be coming up with all this independently.
Another thing: Because it's such a cliche, stories about abuse will attract a lot of negative reviews– Fan-fic authors get very upset at this and defend their stories hotly, but I've
never known one to use the grounds that it all happened to her. I know many former "Suethors" who tell me they put all the trauma stuff in because, well, everyone else did and they kind of thought you had to. In fact– I'll come clean– I've produced some pretty melodramatic stories myself!
In fact, judging from my own travesties, I think the other thing at work here is that young writers know that you're meant to give the main character some kind of adversity to overcome, but they just haven't learned any sense of moderation yet.
Edit: I'm not saying every fan-fiction is terrible. There are some very good ones around. It's just that I deliberately seek out bad ones...