I think this is just a tough spot for any of these kinds of companies to be in. It's easy to suggest that they should just ban or allow filtering out AI content, but the problem isn't that easy to deal with. Adding a manual "AI generated" tag stops being useful as soon a negative consequence exists for using it.

It brings to mind the issues with AI content on Pixiv. They added this tag and then made it possible to have AI generated stuff not shown to you. So, now, it's pretty common for users to not tag their AI content, and it's pretty hard for companies to keep up with the flood.

If they want to remain open to small time artists, they don't really have any choice besides labeling the artists they know to not be AI.