Newness is what gives art, writing, news articles, discourse in general, its value. stable diffusion, GPT-3, etc are simply generating aimless rehashes of what's already been said and done.
example: check out a daily newspaper, online or off. most every sentence of its news articles are based on new facts personally witnessed by the writer in the past week, expressed with the maximum of economy. where's the room for an AI there?
Or fine contemporary art (the kind people pay for). This category of art inevitably incorporates things like commentary on previous generations of art, rejection of previous forms, questioning what an art form is, etc. None of these things can be done by Stable Diffusion's pastiche of genres and influences.
Quickly artists will begin incorporating Stable Diffusion and its implications into their work - but they will create value only by doing things like commenting on it, questioning it, perverting it and rejecting it. And doing so will quickly become passé after it has generated some eye popping art sales.
Of course nothing ever generated by Stable Diffusion will have a dollar value on its own, what it outputs is the very definition of a worthless commodity.
For an earlier example of this phenomenon, check out the work of 80s artist Mark Kostabi, who created his own Stable Diffusion-esque entity in the form of a studio of hack artists who created an endless conveyor belt of oil paintings based on his whimsical, banal specifications. They were terrible and Kostabi was variously viewed as a genius and a laughingstock.