It's a market for lemons [1]. The issue is that if AI slop can't be readily distinguished from real human content, the real human stuff will get less and less attention over time. With less attention, people lose interest in writing, and eventually abandon the community altogether. As genuine human writers leave the community, the concentration of AI slop increases, and readers begin to realize that there isn't anything of value left to read, so they depart as well.

[1] https://en.wikipedia.org/wiki/The_Market_for_Lemons