It can only index stuff that's on the Web. Stuff on the Web is, contrary to what is popularly asserted, only a tiny fraction of all human knowledge.
I think people are forgetting how bad search was before Google. Google drove Web directories to extinction. Remember Yahoo!? Back in that era, if I were looking for something as simple as the University of Michigan, I clicked and drilled down through a Yahoo directory. The obvious search query would have been useless. Google changed all that.
I view Google as the yellow pages. It works well for that. Is it an oracle of knowledge? Of course not. How could I possibly expect to find knowledge on a place where there is no reward for making it available? People producing knowledge don't work for free.
I've tried ChatGPT and it's no better. It serves up stuff that is flat-out wrong.