They went so far as to only hire travel nurses (temps), who were commanding 100k+ salaries, when things got bad enough rather than filling a full time position. And, to add insult to injury, the nurses themselves have been getting salaries in the 30->50k range. So HR could have literally filled 2+ positions for the cost of a single travel nurse.
That's what has lead to a nursing shortage and burnout. HR cost cutting because "we just need the minimum and no backups". It's a big part of the strikes.
Believe it or not, many nurses and doctors working in healthcare actually care about their patients. Something HR is more than willing to exploit to get them to work ridiculous hours.