If there was something better out, wouldn't it be safe to assume that people would play that over a game that wasn't as good?"
No. First of all, you should never assume anything. You are commiting some major faulty logic here. Secondly, just because something is popular DOES NOT mean that it is the best. Britany Spears sells a lot of albums, yet her music is considered by most music critics to be crap. I'm not saying that CS is a bad game. But it isn't the best. The main reason that it is so popular is that it was the first big mod. Everybody knows about it. It has gone retail... you see it in the stores. Advertising has a huge effect on what gets played, bought, watched, etc. CS gets far more exposure than any other mod, thus more people know about it, therefore more people play it.
Or just go back to playing sims.
I don't play "The Sims" if that is what you are saying. That game got boring after about the first day. I am a hardcore gamer who plays all different types of games and am generally pretty competant at them.
I used to be better at CS than I am now. If I didn't get at least a 3.5 to 1 kill ratio I was having a bad day. Now I play it less because I play more DOD. But actually I haven't been playing FPS much lately, or any games. School taking up too much time. But I am an Official Beta Tester for valve, so I don't think I quite qualify as a noob.