Or they're protecting themselves because they're immunocompromised. Or because they are. Or because a reduced risk of catching a pretty annoying disease - both short and long term - is worth it to them.

Tell me, do you wash your hands?

It's weird that mask wearing is a political identity in the USA.

Maybe some people care more about protecting their brains than about what political statements people might think they are making?

Or maybe they're sick?

That would be kind of them. Most people don't mask, even when they're sick.

But also, even if healthy, maybe they're immunocompromised.

A family member of mine worked in a highly political field, and she once participated in a video call where the host, who was alone at home, wore a facemask throught the entire call. Everyone had to put extra effort into making out what she was saying, and it impeded with the automatic captioning system, all so that she could broadcast her political affiliation.