It's a very "boomer" decision. I mean, I can understand Valve trying to protect their users against the unknown, but blockchain games / play 2 earn / metaverses are pretty much the future.
Just imagine VRChat with unique collectibles, immutalized on a blockchain like Ethereum (so the item and the owner is completely verified), and being able to trade them for real money.
It's like when Diablo 3 had a real money auction house. They were early, we still are, but these kind of game features will be the general norm in some years.
So Valve will probably evolve in the future and accept them, when the space looks safer.