Xbox Arcade Games

System: Xbox 360

I know that the xbox 360 vault is fairly new and still growing but I was curious as to why vimm's lair and/or redump have so many games that aren't listed (to my knowledge) from the xbox arcade marketplace; zombie wranglers, crystal defenders, the dishwasher, just to name a few?

P.S. I notice this a lot with indie games as well, but that's a bit more understandable.