Valve will let players (including kids) gamble on skins because it boosts player count. According to them.

Big publishers will still give you rewards for signing up somewhere, entering something, going to an arbitrary website and watching their stream, etc.

But for the small devs: you’re not allowed to even give a player a reward for watching an ad. The choice doesn’t even matter. It just can’t be done.

It’s a private corporation so Valve can do whatever they want though.