One thing I don’t get is tho, why so many of these manga involve rape?
It's a very lazy way of giving a female character a Dark Backstory™. Manga doesn't have a monopoly on it, western movies, books and TV series use it as their go-to buried trauma all the time.
Does rape by a man turn someone lesbian?
Some authors think so, yes. And people at large, believing that being lesbian has more to do with "rejecting men" rather than "being attracted to women". It's bullshit of course, and thankfully less common these days as lesbians are more visible, but the idea still floats around and lazy writers still use it now and then.
I can see how people who buy into "pseudo-romance specific to adolescence" would believe in it though.
