I only have 20 champs cause I join LoL like in mid August, and I'm a free user right now. Yes, I know I can buy champion with RP, with real money, but I don't want to. There are three reason why I don't want to buy champion pack:
A. Buying champion pack will introduce a bunch of new champion, some of which I may not enjoy playing but will now have to put up with because that champion is on my account now.
B. Buying champion with RP, which is something essentially free because you can buy it with IP is kind of a wasteful in my book, and I just don't want to be that guy who throws in hundred of dollars into a game buying content that could have been grab for free and over commit himself to that game. Skin and decorative item is another issue, which brings me to my next point.
C. Due to constant dc/lagging of LoL, I don't feel comfortable making any sort of purchase in LoL. Honest to god, every-time I thought about making a purchase, Riot immediately gives me a very good reason not to, i.e: more dc/lagging. Riot support, if you're reading this, fix your god gamn server, it's chasing away customers, and I'm sure that's not your intent.
(P.S: before someone jumps in and says that I should check my connection, I did. And so did the tech support from my service provider, it's definitely Riot's server problem.)