I don’t know for sure, clearly, but I’ve seen it speculated in a number of newspaper articles by now, e.g. this in the FT:
“The final — and most controversial idea — is that genetic change is making the virus less virulent as it passes through human populations. “Viruses are prone to mutate as they move into a new host: human beings,” said Prof Openshaw [professor of medicine at Imperial College London]. “Mutations could produce more or less severe variants but theory suggests that on the whole they are likely to be less severe.””
https://www.ft.com/content/c011e214-fb95-4a64-b23c-2bd87ebb29d7
I’ve just been checking the deaths numbers every now and then in a few countries to see if they’re going to start ticking up yet as per cases and it just doesn’t seem to be happening. Schools have even started again as of 3 weeks ago in Germany, so there would certainly be mixing and spread from that across people and age groups, but still no uptick in deaths again at all.
Mutation isn’t the only possible reason of course, but somehow it definitely seems far, far less dangerous currently than when it first appeared.