There were multiple bus loads of people showing up every day. They weren't "phantom humans" they were real people trying to find asylum. Many left once they arrived because the city offered them bus tickets elsewhere. Some ended up being temporarily housed. Some just needed to get to a Western Union to get money and were completely independent.

The reason this shelter stayed empty is because by the time it was built Texas and Florida stopped sending busses. Remember that this crisis for NYC was entirely manufactured by other state/city governments. Once NYC made the investment to handle it, they stopped the crisis.

This stayed empty because by the time it was set up the busses stopped coming. As soon as the city was adequately prepared for the multiple bus loads of migrants coming every day, they stopped being sent.