Comment by Vinnl

Makes sense that that's the case: there's usually a limited amount of beginner's knowledge, and then you get to the medium level by arbitrary combinations of that beginner's knowledge, of which there's an exponential number, making it less likely that someone has produced something about that specific combination. Then at the expert level, people can get real deep into some obscure nitty-gritty detail, and other experts will be able to generalise from that by themselves.