Especially Valve's? If anybody I would expect it would be the developer of the game itself would would care, not Valve. I see no reason why Valve should "step in" here. There doesn't seem to be anything to "step in" about.
Valve are a retailer, and as such, they should be expected to care about the products they sell (Nb: I do believe the original developers are the ones who should care the most). I'm sure Valve do not want to garner a reputation for selling poor quality mods any more than developers want to gain a reputation for allowing poor quality mods for their games.