Just taking a look now. 12:46 (so just past noon) at JFK and there are 9 aircraft on the ground.
Flew over to La Guardia, noticed 3 aircraft in the air on the way over. At La Guardia 10 aircraft on the ground.
On the way to Newark I got 4 traffic warnings.
At Newark there were 7 aircraft on the ground.
Then I hopped to Atlanta where I spotted a dozen aircraft on the ground.
I have traffic density set to 100%, which might have something to do with it.
Also, if you wait a few minutes the traffic will start to appear. Sometimes it takes a little while for everything to develop.
So the traffic is there