Responses
I mean, you have a point. It sells like that, because nowadays it's all virtual, noone has to know what you're buying anyways. Imagine going to a bookstore to try to buy this, tho lol. But, even though we were just joking here, I think that also has to do with the romantic nature of yaoi's target audience (women). We usually prefer(ed?) a subtler approach and a deeper connection or subplot between the characters to enjoy it, even if it's smut (which is why you'll find them forced-saying they love each other even when it's a one night stand, for example).
I remember back in my day where titles were simple. Where you could read a manga named " Blue Sky" and have it not actually be about a blue sky. Now these youngster come on in with these new long fancy shmancy titles that tell ya everything god damn thing. Whoa is me! Where did all my subtle/metaphorical titles go?