Gay in porn, asexual in real life. What gives?

I'm a guy in my early 20s and I can't remember ever having a crush or being sexually attracted to anyone (male or female) in my life. However, when I watch porn, I always get turned on by guys, especially seeing bubble butts, them frotting or tongue kissing. I've tried looking at guys in a sexual way in real life but I can't really get it up like in porn. I don't look at guys on the street and think 'I'd fuck him'. Same goes with girls.I've also tried looking at girls boobs and butts but I don't get a reaction. It's been like this ever since I discovered porn in my teens. What gives? Is there something wrong with me?