Bigots are incapable of thinking this way. They only see LGBT+ people as “the other” and themselves as “normal”, so they never realize that they themselves at one point figured out their own identity (including both gender and sexuality). They think it’s only LGBT+ folks having to figure those things out.

It’s bizarre, especially since society does push cisgendered and heterosexual norms at a very early age. Young boys will get asked if they like any girls and they’ll constantly be pushed with gender roles and stereotypes for their birth gender. It’s so normalized that most folks don’t even seem to realize that it happens until confronted with the existence of any alternative (like LGBT+ folks). A reasonable person would examine their biases and realize stuff like “huh, I guess I knew my gender from a young age”, but bigots have this irrational hatred for LGBT+ people so they’re not willing or capable of this kind of insight. Their brain has to twist logic into justifying the bigotry that they’ve already concluded on.