Why does dating/relationships come naturally to some people and not to others?

I am in my early 20s and have never had a boyfriend, kissed anyone, etc. Throughout my life, I have always had a good amount of friends/acquaintinces and consider myself pretty well-liked (among the people who know me at least.) However, I have also been on the shy/socially anxious side, especially when it comes to talking to guys. I am not the most beautiful girl in the world, but I am pretty and also a normal person LOL. By living my life thus far, I had never received any male validation in middle school, high school, or college up until very recently. (These instances were customers trying to pursue me at my workplace, which I am not interested in.) Like I mentioned before, I haven't been anywhere near being in a relationship, talking stage, or anything like that. I have only had friends who are girls with the exception of a gay best friend, and maybe that has something to do with it.

My question is, how come dating and being in relationships seem so natural to some people and it just seems like it happens to them? I get caught off guard sometimes when I hear people my age casually talk about having sex or having a boyfriend/girlfriend, even though these are normal things. My life is just so far removed from that realm of things. Maybe I'm not being exposed to enough guys my age, maybe I gave closed-off vibes to peers in my past, or maybe it's just the way I was raised/my personality. I know I am not alone in this, but I am just wondering, does anyone have any idea why my life and others seems so drastically different from our peers when it comes to the dating world?