For the first time in its 115 year history, New York City deliberately shut down its entire subway system, to deep clean every subway car

The cleanings will be done on a nightly basis, from 1 a.m. to 5 a.m. When the cleaning is done, every single subway car will be disinfected.

My question, is why did they wait until now?

https://www.cnn.com/2020/05/06/us/new-york-subway-closed-history-trnd/index.html