It's all the elective surgeries being cancelled. They bring in a lot of billing dollars to the hospital. The hospital's budget is built to have those dollars. Sadly, I don't think that the care for a COVID-19 patient brings in the same amount of billing dollars. While ICU's are expensive and generate a lot of billing dollars, they are usually fairly full anyway.
Another problem for the hospitals is the outpatient surgical centers that they own. Those are also shutdown and also bring in a significant amount of revenue that the Hospital counts on for its budget.
Lots of hospital's have a group practice that they own that provides family medicine, and other routine care. Some are shutdown due to staff being redirected, but others aren't seeing much patients. People are scared to go to see a doctor about a little thing because they think they are going to get it.
In our city they are setting up a 250 bed field hospital in the convention center. It will handle COVID-19 patients that need minimal hospital care but can't go home yet. Similar to a high end skilled nursing center. It's a step down facility since the recovery period of a ICU COVID-19 patient is a long one.