For Valve, it's simply business and a way of making money that hasn't been outlawed yet. Yes, it preys on younger people and those who don't make good financial decisions. However, a lot of the people who participate in CS:GO cases are simply looking to make a profit. Whether it be trading your way up, scamming people who don't know any better, or simply getting lucky, there is possibility to make it worth your while. Also, some CS:GO players are very committed to the game, and don't mind spending a few bucks to have some fun with what is essentially an in-game casino. Especially when the rewards entail having customized weapons in-game and a perceived status booster.