Really good question. One hypothesis is that they're massively under-testing, but there's not a lot of data to support that. If you look at https://covidtracking.com/data/ for example, you see a positivity ratio of about 9% for FL, compared with 86% (!!!) for NJ, where it is really clear that the situation is dire but we're not seeing it because of lack of testing.
The other one to watch is Michigan. There the "data quality grade" from covidtracking is a D.
I think Iceland pop 300,000 tested everyone. The result is 50% of the cases are asymptomatic. That's terrible in two ways, one is potentially it's spreading undetected. And two natural herd immunity comes at an enormous cost.
The other one to watch is Michigan. There the "data quality grade" from covidtracking is a D.