Speaking for myself, having agreed with Jessica’s sentiment in a comment just above, I stay because the United States is my home. I have lived abroad and enjoyed it, but as much as I dislike what’s happening here right now, this is my country. My people are here. My heart is here.
But more to the point, if all the good and decent people left, then what? Nothing good, that’s for sure. Positive change is always brought about by doing hard work, not by going someplace where people have already done that work.