What these sorts of bans and closings do is slow down the rate of transmission. By limiting opportunities for people who are infected to interact with large numbers of other people, it spreads the total number of infections out over time so that at its peak the system isn't overwhelmed. It gives health care professionals the best chance to use all of the available resources to help those most at risk, which are always the very old, the very young, and those who for other reasons have weakened immune systems.
It sucks that it's going to affect March Madness, but a month ago it would have affected the Super Bowl, and it's most likely to affect the start of baseball season.