At this moment of my life I really don't understand why people collect or pay money for some shitty games
For me, there's several reasons:
1) The games are great to riff on MST3K style. It's great to get together with a group of friends heckling each other and the game as we try to play games like Superman 64 or Pimp My Ride.
2) It makes me appreciate the good games more. When you take some of that garbage and put it next to something polished and well designed, it makes the good games feel all that more impressive. I also like to use them as pallet cleansers, so my gaming experience is not diminished by me still being mentally attached to the last game I played.
3) It's hilarious to have the games in my collection. Being able to produce a copy of Hannah Montana or Bratz: The Movie at will is well worth the pennies I've spent on them.
4) The gamerscore. I do like my achievements, and those shitty games provide points just as well. Though some can actually be surprisingly frustrating to get the full completion. It's also interesting to see how few of people actually bother to go the distance and finish those pieces of trash. I for one, have actually earned the full set of achievements for "illustrious" games such as Barbie Puppy Rescue, Monster High, Space Chimps, Shrek the Third, Spiderman: Friend or Foe, and Darkest of Days to name a few.
Right now, I've been bulking up the crappy title collection for the DS the most lately (namely as I'm about out of 360 titles). I should be seeing my copies of Discovery Kids Kitten Corner and Imagine: Ballet Star in the mail pretty soon.