This is true on its face, but think of what the tournament actually is: almost a month of college basketball programs traveling around the country. Even if the arenas are sparsely crowded, what are they doing in a city that isn't home? Going to restaurants, staying in hotels, etc. If they planned to go back to campus in the interim, many are shifting to online only or are straight up closing for the time being.
This is all leading to the central issue of what would happen if a player or coach was diagnosed - the answer to which is that the team would be quarantined, unable to participate, and the fairness and integrity of the tournament itself would be called into question. That's not some crazy scenario, I would argue that is probably an even-odds outcome right now. Canceling the tournament midway through after jeopardizing student athletes is a pretty bad result for the NCAA.