They're publishing machine checkable proofs because that's the only way they, themselves, can check them.

They don't understand the math either.

For 3.5 days we had a machine checkable proof the Collatz conjecture was false. There turned out to be a bug in the machine checker.

Yes, however any LLM agent you asked about that proof could tell you that. (And even most humans who know a little bit about the bug.)

You are right that Lean isn't great in this respect, and people are working on proof formalisations that are less prone to bugs.