If you ask them they always have a reason but the real reason is that they're irrationally afraid of a now-endemic virus that they've probably already been exposed to. If you're not ripping the mask off first chance you get it's most likely because it gives you psychological comfort like a blankey or a teddy bear.

edit: and that would be fine if you assholes hadn't spent two years shaming people that they were killing grandma because they didn't want to wear these inneffectual face blankets. They don't work, they never worked. Their only effect is to make neurotic people feel better and/or superior. So it's no surprise that, lo and behold, 'long covid' is actually just neuroticism.