AKA selfishness.**edited for clarity**
While I may not necessarily agree with them, I'm not all that surprised by people responding so negatively. American culture greatly values personal freedom, it's just the way it is, so when people are told that they can't go somewhere without wearing a mask, or that they have to stay home, they don't react well to it.
If they made masks mandatory, then people would really argue that it's going against their freedom, and they would wear masks less. Americans are contrary by nature, if you try to force them to do something they're going to not do it just because they don't like being told what to do. It's like what America was built on, to a certain extent. That's part of why everyone's so upset about the forced shutdowns to begin with.