If valve was actually permabanning people for cashing out, you wouldn't see it as basically the primary way people interact with CS:go.
Because at that point it's out of their control, they can't tell when someone trades a skin or item to someone else in order to cash it out through a Paypal payment, unless everyone were to start posting on the forums about how they just cashed out their keys or weapons. You can't hold them responsible for this specific action that takes place outside of their control. Sure, the trade system may be part of the Steam ecosystem, but it's impossible for them to tell the circumstances under which a trade is made.
Tons of people use the Marketplace within the Steam ecosystem, need some numbers to prove people cash items out enough to claim that's how they primarily interact with the game.
Hence the wink and nod. They don't discourage it at all either. they don't care. They don't give a single fuck if you cash out, because to them the money is theirs already. When you cash out, using any site, they're then using your valve spacebucks to buy things like keys (which valve again gets another percentage of them doing this), and then sells the keys on something like g2a at a slightly cheaper value. Valve doesn't care about that part because it's a key they ALREADY SOLD.
Sorry, just now I saw your reply to me on that post. I updated according to replies from others, it's actually against their ToS, meaning they do have a stance against it (and so there is no wink and nod here). What I just wrote right here ^ also applies to this.
