In some ways the denial of bottoming at all is part of the allure of masc heteronormativity. It's oxymoronic.
it is more of an american and middle east thing?
hereroflexible straights in west europe mostly want to experience as a bottom if they are with a gay or bi man.
And this makes fully sense to me in case they want try sth new.
also, when you want to fuck a male as a „straight“ guy you need to be somehow stimulted by a hairy, male ass and get a hard on.
as a bottom you don‘t need to get hard that and you can concentrate on the anal experience.