It's true, I've also used the likes of Unsplash, but with AI art, the ownership falls onto the person that gave the prompts in the first place, potentially shifting the value from "cheap" to basically "free" in the market. Why pay the artist, when you can describe what you want, get it done in mere minutes and only pay the price of electricity your PC uses, while having full ownership of the generated artwork? As AI evolves to be more creative, detailed (and also better in drawing text), I believe this will be a real problem over time, starting from generic work, as "placeholders".