This is a really interesting question that I don't pretend to be an expert on. It probably comes down to what causes the difference in reaction to the infectio

This is a really interesting question that I don't pretend to be an expert on. It probably comes down to what causes the difference in reaction to the infection. It could be that there are differences in people's immune systems that cause them to have a much more severe reaction. In this case the quarantining wouldn't have an effect. If people who are having a much more severe reaction are getting a strain of the virus that has mutated to cause these more intense symptoms then you would see the issue you are talking about. My uneducated guess is that it is the former, but I'm really not sure.