OK, I am not hung up on whose gay and not gay and whose bi and all that BS. It is generally true, I think, that most men associate anal penetration with homosexuality. It is also generally true, that most straight guys are not too sure what a prostrate is at least until they get cancer there. Straight guys are, I feel, mostly unaware of their pleasure centres and are focussed too much on other peoples appreciation of length, width and duration as opposed to the myriad other things that make a partner enjoy themselves and social stigma (which I feel is in itself self imposed) prevents many paths of experimentation.
I got over the anal thing (being a straight guy) when a lovely young lady stuck a little-finger-vibrator up my bum while having sex with her....now I just have to get over buying one.