It's basically an addiction.
It started from rebuying stuff I had stolen in a burglary, then regetting stuff I had as a kid, then the stuff I missed out on as a kid. Coupled with my interest in tech and gadgets I had to get the latest gen too.
Somewhere along the line, it turned into needing to complete series of games. Add to that, drunk online purchases, browsing when bored, and buying up lots. Once you get to almost 3500 games in, it seems impossible to stop! Lol