- if OpenAI publishes 100 proofs of big theorems - verified using Lean, but not carefully written and not properly citing previous work - it'll be worse than if mathematicians have a chance to take this work, see what they think about it, and turn it into properly written mathematics before it's released.
You say "we also have the option to ignore them", but few mathematicians working on a field where the blah-di-blah conjecture is a central open question will simply "ignore" a proof or disproof, verified using Lean, of this conjecture. Some may ignore it, but the others will will go on and use this new research. We can shut our eyes, but publicly available facts don't disappear.