I read somewhere recently that if as few as 10% of drivers obey the speed limits, especially in an urban environment, that almost all drivers end up obeying the limit (give or take).
In the current climate, it may just be that the '10%' are staying home, and thus their slowing influence is being lost.
That is an explanation that makes some sense. Or at least that the 10% are driving less. They are likely to be the folks who are more cautious, and more conservative about accepting risk, and will also be the folks who are more likely to stay home as much as possible, only shop locally, etc.