I believe that they are shutting things down due to the influx of hunters into the area, even if there is only a couple hunters per square mile.
Most of these areas have a very limited health resource and if someone comes in that has the virus and becomes sick he may have a problem getting the help that they need, and if two or three come down with it then it can become even worse.
I can see both sides of the argument of letting hunters hunt and for the closing and limiting access or closing hunts side of the argument.