The S&P crashed 35% before going up again, and is still significantly lower than it's high a few months ago. So I think it is more that the virus is not as bad as we thought a month ago (which seems to be true - projections in the US and Canada have gotten significantly better over the last month). The market does not go up or down when we get bad or good news, it goes up or down when we get news that is better or worse than expected.
Also, the S&P 500 is made up of mostly large companies, many of which could benefit long term from the virus. Sure in the short term there will be a revenue hit, but in the long term if their smaller competitors can't survive that hit and they can, they will become more dominant in the future. As far as I know, small business indexes have not recovered much.
The virus's effect on the US economy is significantly worse than it was estimated to be a month ago. Back then the thought was that we'd be fully operational in a few weeks. Now there's increasing evidence that we may be economically degraded for months or years.
Also, the S&P 500 is made up of mostly large companies, many of which could benefit long term from the virus. Sure in the short term there will be a revenue hit, but in the long term if their smaller competitors can't survive that hit and they can, they will become more dominant in the future. As far as I know, small business indexes have not recovered much.