The same thing sort of happens with humans teaching humans though: you get things like linguistic drift where the structure of language and the meaning of words changes over time, and artistic styles and musicial fashions gradually shift as well. What's different here is that there's an ouside reality of what (for example) faces look like which human perception is grounded in but AI training doesn't have access to unless it's added to the training data. This means we also probably shouldn't worry about humans consuming AI generated stuff having the same effect, since there's no reason to think it should be any worse than humans consuming human-produced stuff.