My own personal health is such that I wouldn't have to be so conservative if I were thinking only of myself. But Covid isn't just symptomatic, it's also contagious, as in, I can pass it to others who may not be able to handle it as well as I can, including those that aren't merely antivax. So the idea is more that if Covid is doubling at some rate, I limit my social activity so as not to contribute to the spread.