You know all those famous problems that were solved recently? How do you know they were actually solved? Maybe the Math professors are just pretending to check each others' proofs, playing a gentleman's game, and they don't want to admit that these achievements were wrong?
How do you know? Do you really want to spend 5-10 years learning enough to check one of these proofs?
If it's a computer-generated proof, and people checked the source code but can't read the proof (because it's terabytes of details), is that a valid proof? It isn't really leading to any greater understanding.