They weren't ultimately needed then and you couldn't staff them now that the pandemic is countrywide rather than restricted to NYC. The real limiting factor here is availability of trained medical personnel and there is no surplus of them anywhere.

> earlier this year we had setup unused overflow facilities and those were taken down.

No, they mostly weren't.

> Why were they dismantled?

They have largely been activated, including ones which while prepared stood empty in the initial, far lower, peak, and many additional ones were set up for this surge.