The simpler explanation--they know the virus is most likely not dangerous to themselves. But they care about others, have empathy, and don't want to have anyone

The simpler explanation--they know the virus is most likely not dangerous to themselves. But they care about others, have empathy, and don't want to have anyone else's death on their conscience, and think we should all work together on this. To those without empathy or conscience, these people seem to be doing something silly and theatrical and it mystifies them.