Because companies don't care enough or they're unaware, really. Some of them might even appreciate the brand recognition, though that'll be a minority. For example, the people at Spalding might not be aware of such sites. Sure they have (perhaps) some deals with E.A. about branding, but the people there working at…
Not really, they cherry pick what they want their product to appear in, or depends on how well connected your cousin is to a guy in the place. For example, the game HomeFront had to struggle with the ingame Ad's since not many people, even Hooters, wanted to put in a game where Dystopian settings is the norm.
I would actually think that companies should love to have their products in games (of course without getting into the whole association with violence ect.), since it's free adventising for their products. Take for example Pepsi, wouldn't it be great for them if the games showed Pepsi cans ingame instead of noname/fictional…