I started collecting over the years, not so much for the sake of collecting itself but instead to be able to play the games I was buying. It's hard not to acquire a collection if you're a gamer. Unless you trade in games everytime you buy a new one.
The last few years I've bought less and less games, as I already find my collection big enough as it is. I don't want to possess a collection that starts to "own" me because of its sheer size. I "only" bought 32 games in 2013.
Ocassionally I've contemplated selling off my older systems and games, as I raraly play them. I do virtually all my gaming on systems of the PS1 era and newer. What's stopping me from selling? I guess the effort of actually putting everything up for sale and the vague belief that prices will rise in the future.