Why are hospital nursing shortages structural rather than market-clearing?

Genuine puzzle. Nurses are in shortage. Wages have risen but not as much as you'd expect for the shortage. Hospitals continue to operate understaffed rather than pay through the shortage. My read: hospital revenue is fixed by reimbursement formulas. They can't pass increased labor cost on to customers (patients/insurers) the way most industries can. So they prefer "running short" to "raising wages until the gap closes." It's a constrained-revenue version of monopsony. The bargaining structure of nursing makes it worse — most nurses don't have collective negotiation power outside specific markets. Travel nursing was a temporary workaround that's now being unwound. Curious if anyone has a tighter model.