Academic venues don't have enough reviewers. This problem isn't new, and as publication volumes increase, it's getting sharply worse.

Consider the unit economics. Suppose NeurIPS gets 20,000 papers in one year. Suppose each author should expect three good reviews, so area chairs assign five reviewers per paper. In total, 100,000 reviews need to be written. It's a lot of work, even before factoring emergency reviewers in.

NeurIPS is one venue alongside CVPR, [IE]CCV, COLM, ICML, EMNLP, and so on. Not all of these conferences are as large as NeurIPS, but the field is smaller than you'd expect. I'd guess there are 300k-1m people in the world who are qualified to review AI papers.