The reason for this is that mathematical papers are fundamentally about an insight about mathematical objects. The insight typically comes from the mathematicia

The reason for this is that mathematical papers are fundamentally about an insight about mathematical objects. The insight typically comes from the mathematician having a deep understanding of the mathematical objects. The theorems are some formalised statement that should be true based on the deep understanding. The proofs are something else entirely, a sequence of steps which combine to verify the theorem but where many steps may result from trial-and-error searching for a path forward. Coming from a good mathemematician, the original insights are much more likely to be correct than the details of the proof steps.