It's just a way to explain away all of the false positive tests. They don't want people to think about what the false positive rate would really be (false positives being 90% of the positive results), and have to explain that if you have it there is only 90% chance that you would notice. The other issue is that if you are "asymptomatic" you are not contagious. There was a theory going around early on that you might be contagious anyway, but that was just an attempt to play it safe in case it were true. It looks like it is about 90% certain that it isn't. Now they need to think that most of the spread is occurring asymptomatically because "it keeps spreading," even though that just means the list of false positive cases is growing with time. The number of deaths per day shows no growth. It is less than it was in March. You have to go all the way back to February to have a lower death rate.