If money is involved, the whole magic of modding is gone. The freedom of creativity within the community is broken. The workshop here is what gave these games longevity. It expressed the creators talent and expressions. It was a place to start for some, a place to learn for others, etc. Money involved just weakens all of this in my opinion.
Edit: Following up from what Sjonsson and FMPONE said,
I do agree, from a freelancer perspective much like a Youtuber/Streamer, which I was not thinking about earlier; if the market is truly large enough now, its great people could start making decent income doing what they love within the comfort of their home. I hope its somewhat regulated though. Like other people have said, it could be risky to buy some of this stuff and not have it work, or whatever reason.