I'm going to play devil's advocate for a second.
The number of cases are way higher - Former FDA head Dr. Scott Gottlieb estimates we're diagnosing 1 in 10 to 1 in 12 cases right now. At 58k positive tests yesterday, we should estimate (lower end) that ~580k people would have tested positive if everyone went to get tested and we had the capacity. The Mississippi governor is a math guy but he completely left this part off of his equation.
On your comment - "The highest estimates are 20,000,000 Americans have has the virus. If you assume the virus has been here for 6 months that's 111,000 cases per day. At that rate..." This isn't accurate or a good way to look at it. It completely negates the exponential growth of a virus, this hasn't been and never will be a linear growth. That's why we're so worried about overwhelming hospitals too quickly.
If 40% (128 million) is your target, and we've already infected ~20 million, and we're infecting conservatively 500k people per day, we're actually not far off (about 200 days). This is all to say we're going to continue infecting 500k people a day because we are refusing to wear masks. We should wear masks or we'll be stuck at this very high plateau of infection. It's pretty simple.