maybe cause they feel taking it from behind feels better than the front?? idk
Probably, but mainly because the author likes him being uke and wants to tease us lol XD
By "tease us" I meant that most of the new manga have thing "hinting" towards a seke relationship but it never happens. It's like a trend now for the uke to want to be seme for once but the seme to not want to be uke. At least this is a little different, but it's still annoying to wait for it to happen and it never actually happens because it's all teasing to make the story more interesting or/and to make us keep reading...
That's the issue I have with these type of story. They make it a plot point to tell us that he wants to loose his virginity... but then when the times come, they don't tell us why he wouldn't do it...