Well I finally looked into this (with Copilot).
https://copilot.microsoft.com/shares/8c ... 9mUZ1SUQMJ
Basically impact tools shear off the oxide layer that quickly reforms from any mechanical abrasion (which is what makes it resistant to rust), and the hardware essentially cold-welds itself. Then it's done for. So I need to stop using impacts on stainless hardware. Or, I need to use anti-seize which is hilariously counterintuitive since I likely went out of my way to buy stainless in the first place.