I assume if Valve has to expend effort handling refunds, it's best not to sell (or treat them the same way in the store) products in regions where it could cause issues.Valve doesn't enforce its own ToS why would they act on behalf of Sony without their permission to delist a game based on Sony's own Terms of Service?
I think you don't realize how hands off Valve is with third party games on Steam. They will NEVER without permission from Sony do anything to Sony's games unless Sony is doing fraud blantantly.
I think most manufacturers don't care if an end user buys something they can't use, especially if the distributor or store has to deal with the customer. So it can often fall to the distributor to make sure things are in check.