Err, because the majority of the viewers are female audience? I don't wanna be called stereotypical and invoke the rage of people but that's something that is generally perceived. Beside Naoto isn't feminine. The pure gentle type?
Anyway you do realize seme and uke roughly means attack and submit.
You should have the rough idea.
Sometimes it's funny to see English speaking audiences called reversible couple seke or switch. Hahaha.
being sweet, gentle, sensitive etc. are feminine qualities though? a guy can also be feminine nothing wrong with that. all i'm saying is that i find it strange for people to determine the top/bottom positions based on how masculine/feminine the characters act/look. i don't see anyone wishing the characters would switch in the stereotypical girly uke x manly seme bl but when there's a top who doesn't have those huge yaoi hands and super masculine face all of a sudden everyone wants to see him bottom. are you guys trying to self insert into the uke or something?
i think it's basically the general/majority preference by the readers especially that most of the old BL mangas has been centered around that idea for so long
there has been more and more works about an uke that is bigger/more masculine/more dependable/dominant than the seme in the recent years though
ah i myself personally don't like seeing the tops have sex with just that smirk on their faces, no sweat, no blushes (really common in old works tbh). most of the time they look like they're just playing around with sex. i really appreciate when tops get riled up and get heated when having sex with their partner
i like seke couples sure but why is it that everyone's okay with super manly dominant seme x weak blushy girly uke but the second they see an even remotely feminine top they want it to be a switch couple