Two points.
1. Normalization is partially a reflection of what's considered acceptable and what's considered taboo, like you said, but it's also a reflection of what's common. If all you've ever seen in your life are blue cars and all of a sudden you see a red car, the red car is going to stand out to you, even if you have zero moral or religious or cultural or any other sort of objection to red cars. There are neighborhoods in this country where half the people are LGBTQ, and there are neighborhoods where no one is. In those neighborhoods, and for kids who have lived in them their whole lives, it's something that will *stand out* even if it's not seen as *taboo.*
2. Oh the topic of why homosexuality is seen as more sexualized, I've been thinking about it and I have a theory. When parents introduce the idea of sex to children, it's not framed in terms of pleasure or even romance. It's framed in terms of procreation. "This part goes here because this from the man and that from the woman need to combine inside of the woman and that's where babies come from." It's all very clinical. When you're talking about a same-sex relationship, there's no procreative angle to approach it from so you lose the ability to frame things that way. When you take away the possibility of the creation of children, you're left with sex-for-sex's sake. Obviously there are a lot of straight people having sex-for-sex's sake too, but at least parents have an "out" in those situations