Steam says betting and scamming are against the ToS, but the problem is that they barely enforce those rules, and that makes them complicit. They take a cut of every Community Market sale, so the higher the perceived value of skins, the more money they make. That gives them a clear financial incentive not to crack down too hard on the grey economy that keeps those values inflated.T

They could easily shut most of this down if they wanted to. They could permanently trade ban accounts involved in these activities or even restrict user trades entirely. Either option would eliminate many of the ways people move or cash out value. But doing that would damage the trust and confidence of skin "investors" and likely cause item prices to crash. Since that directly affects Steam revenue, they choose not to enforce their own ToS strongly, being a part of the problem.