Not OP, and don’t feel strongly, but I’ll give my opinion on what might make that happen:
Mask is visible - sign of compliance. You can get a flu shot and not tell your ultra-right-wing friends. Even on the right there is a spectrum of course, and folks march to the beat with certain signals, masks seem to be one of them thanks to behavioral modeling from leadership.
Right wingers who don't wear a mask are not motivated by their friends seeing them without a mask. They are individualists. They do it because they see it as resisting being controlled by anyone or subjugated. They are also heavily anti-vax for the same reason. The amount of pressure there is in public to wear a mask is enough that it selects for individualists as the people not wearing masks.
Mask is visible - sign of compliance. You can get a flu shot and not tell your ultra-right-wing friends. Even on the right there is a spectrum of course, and folks march to the beat with certain signals, masks seem to be one of them thanks to behavioral modeling from leadership.