I mean if you are going to take a 75% cut, well then you can afford to spend the fucking time curating your shit. If they are going to charge that kind of cut, they can afford to have people review the content. Given that they are taking a much larger cut than the dev, it should stand to reason that goes to paying for some work on their part.
Have it where you submit a form to Valve with what your mod is, what it does, etc. They screen it to make sure it sounds like a reasonable idea, and then send you stuff to sign where you declare that this is your work, you aren't violating copyright, you've paid commercial licenses for software used on it, etc. Once they have that, mod gets submitted and then it goes off to Bethesda for QA. They test it to make sure that it does what it says, doesn't crash the game, and so on. Maybe even help fix bugs possibly. If that's all good Valve does a final check to make sure they don't see any copyright violation (maybe an automated system that flags and then a human checks i there are flags to see if it is legit) and it then gets posted.
If they were doing something like that, then ok maybe there's some justification of the price. Ya there's a big cut getting taken, which means higher prices, but you are getting something more along the lines of paid DLC. QA like that might be worth it.
However they were just letting anything and everything get posted. They were treating it with the same indifference as the rest of Steam, which is just not ok.