If I were to take a guess, the reason you're seeing URL's not being indexed is Google only has finite indexing resources, yet AI content generators can generate

If I were to take a guess, the reason you're seeing URL's not being indexed is Google only has finite indexing resources, yet AI content generators can generate a near infinite amount of content. That makes your real content a smaller proportion of the whole web, and therefore less likely to meet the threshold for fitting inside googles finite indexing budget.