Dunno if this has been brought up yet but: if you're still masking and other people see that, you can make them deeply uncomfortable with themselves because they know that they should be doing it too. Sure, some people are well adjusted enough to accept that they're not a perfect person, but others are going to cope as hard as they can by aggressively insisting that you are the one whose wrong, not them. Whether that's by going full COVID denial or pretending that people still aren't dying from it or any of the other things people do, and you can bet they're going to resolve the cognitive dissonance in part by taking it out on you, the person who caused them to feel it.

Same reason people get mad a vegans.