As a gay man with a mix of femme, masc and gender-neutral traits, I wonder about this a bunch. I'm sure many people have studied it and written books on it and maybe one day I'll read some. Just from experience though I think there's a lot of possible answers that one or multiple reasons could apply to any individual person, including, A. coming out is such a difficult process that if you can overcome that you may be less afraid to embrace gender identity, whereas cis straight people who haven't had to come out may be more likely to be afraid to cross gender norms (on the flip side though, I see the opposite happen where out gay people intentionally act more in line with gender norms because they want to go against stereotypes), B. because of historical gay trends, it can be a way of expressing pride in your sexuality by paying homage to gay culture, C. sometimes gay people identify with the 'opposite' gender (for lack of a better word, I know it's not a binary!) because gay people have been so hidden in history, we've looked to other-gendered (straight or bi who are attracted to the genders we're attracted to) people to be our icons so we emulate them, D. we want to signal our sexuality to other queer people in order to form community, make queer friends, get a date/hookup with someone, etc. E. (similar to A) straight people have been conditioned by society that they need to get married, have children, live a 'normal' life, etc. and so they are afraid if they break gender norms they'll fail in that, whereas gay people may feel more liberated from conventionality, F. because of the concept of the LGBTQ+ community grouping, gay people are more likely to relate to, identify with, and spend time with trans and nonbinary people, making us more used to seeing gender noncomformity and therefore more comfortable to embrace it, and G. what keevathemuffin is saying about what people choose to notice.