In the first COVID-19 wave in April -concentrated in the Northeast- the nation was testing only about 130,000 a day. Because testing was largely confined to sick people, over 20% of those tests were positive cases. But the total number of "confirmed" cases looked relatively small back then because there were so few tests.
Today we are testing over 1.3 million a day and about 6.5% are positive, mainly in the Midwest.
A regionally-concentrated 6.5% positivity rate is higher than ideal, but lower than during the second wave in July, which was mainly in the South (and had no visible lagged effect on nationwide daily deaths).
While the U.S. is now doing about 1.2 million more daily tests than were done in April, it should be no surprise to anyone that all those tests are uncovering more known cases than before (and leaving fewer unknown cases).