If I'm the CDC/WHO/Public Health crowd, I'd probably want a little bit of distance between my own doom and gloom projections and the more scientific and definitive studies given that I just recommended very strict social distancing/quarentine measures that are having severe impacts on job losses and the economy. The more time that passes the more that that group can say their projections were correct, but the measures prevented catastrophy. Then they were part of the solution and not the problem.

If I'm the DNC, I'd like this thing to run as long and hard as possible without true data coming to light (if things aren't really as bad as we think), because the Trump administration really botched getting the testing out when we had months (or at least weeks) of lead time based on data from Wuhan.

If I'm the Trump administration and I know it's not going to be that bad, I might be okay with everyone projecting the doom and gloom at the DNC because if it turns out not to be that much worse than the flu then my measured response will age well.

Just speculation at this point, but there are reasons why any of the groups above might not support random testing so we get better projections.