Because it is looking like those who have had this virus are immune after not--not for ever and ever, perhaps, but long enough for us to ride out the pandemic.
And it is looking like large %s of the population in most affected countries have had the virus, with no or mild symptoms. I don't want to debate about what % this is. But it's likely to be a large minority at least.
We need these people up and running so that we can avoid grinding our economies into the dust.
Every stop needs to be pulled out to get this up and running as soon as possible.