Like many of the other people in this topic, I was started on gaming in general by my grandparents. My grandma had an NES and every day after elementary school I would walk to their house down the block from the school and we would see how far we could get in SMB3. Meanwhile, my uncle who still lived there would play the more "advanced" games like Punch Out and Zelda 2. As I grew older, I stayed largely a Nintendo kid, and I would play awesome games like the Megaman X's and Earthbound. I enjoyed being able to play the "advanced" games I admired watching my uncle play. Eventually I got a PSX for my birthday, and that's when I really started to get into RPG's. I used to own games like Tales of Destiny 1 and 2, Valkyrie Profile, Dragon Warrior 7, etc., but I was young and stupid, so most of these games weren't cared for or lost. To add to that, my mother, who is a Filipino immigrant, donated all of my old cartridges to the Philippines. I was devastated at the time, but now I can appreciate the action, and I hope that some Filipino children got the same enjoyment playing them as I did. So, I guess one reason I started collecting was to recapture those moments from my childhood.
Once I went to college I got a part time job a local Gamestop (please don't strike me!), and while the company is evil, it proved an excellent way to start collecting current games. Additionally, I prided myself on being a wealth of information, whether it was a recommendation, a plotline, gameplay tips or just the state of gaming in general. Sure, usually a guy would just come in and bluntly ask for Madden, but sometimes I could actually have a great conversation with somebody about a particular game or game mechanics. I started to write mini articles about games I enjoy, and funny things we expect as normal within the confines of video games. Of course, I feel like I can't really fully speak on a game with any sort of authority unless I've played it myself. So, I guess the other reason I collect games is the pursuit of knowledge.
As a final note, my sister recently had a boy, so I hope that in the future I'll be the cool video game playing uncle :-P