I think mostly all sexual deviations have to do with things we perceive during our development. This has been discussed at length in the medical field, mostly about certain fetishes, and it seems like those preferences have to do with certain stimulating experiences we have as children that leave a lasting impact on our developing minds

Now, most of these are fetishes, not just same sex attraction, but I'm sure that it has something to do with it. Often times it happens to children who are victims of sexual abuse. Those highly emotional and traumatic moments we have as children do manifest into our sexual development, and many homosexuals have been molested in their past.

Or as you said, it's just through exposing our brains to more and more depravity. Next thing you know, you're looking at weird furry incest rape fantasies instead of being able to get off to vanilla intercourse