People are not reinvesting, they're just doing it to increase their steam level. There are minor benefits to having a high steam level, like getting a higher droprate for "boosters", and being able to get a larger friends list, and at some intervals you're able to get some more elements for your profile page on steam, like being able to have an extra achievement showcase and such, but really, it's mainly about getting that number indicating your steam level go up. And this is not a new phenomena. People were buying crap games for Xbox 360 to get achievements, which in turn made a counter go up. There was no real gain to it, all that happened was that a counter went up.