I don't know why,but i feel like giving a serious answer here
If your yaoi tastes expands beyond traps, I think you are probably bi and only just discovering this side of you. Im not sure how seriously you are taking the other replies here,but i felt someone needed to point out bisexuality exists here
In all seriousness though, if you've ever had interest in real life men then you might be bi-curious.
Another though could be that a lot of anime and hentai men have a feminine quality to them so it may be that you are attracted to the 'feminine features' of the characters.
I like reading yuri sometimes, but that doesn't mean I wanna have sex with women (kissed some though). I find women sexy, just not sexually attracted.