Health care is a much different situation than most manufacturing due to the massive involvement of the federal government and the large involvement of state governments in healthcare. The employers are often multibillion dollar multi-state duopolies, and the Medicare rules have pretty much pushed any independents out of business. The state certificates of need laws actually do keep new players out. The hospital systems have a large number of employees with specific and often very expensive training that is only useful when working in healthcare. The employers thus have pretty much all of the negotiating power as all the employees can do is either agree to demands or quit, and if they quit, it is going to be essentially the same elsewhere (due to the federal government's involvement) so quitting really means quitting for good. They either leave the field and end up with completely worthless training or retire if they can.
The main underlying issues causing people to quit in healthcare are chronic understaffing, poor pay, poor treatment by patients, and poor treatment by administration. This is not new and has been an issue causing shortages of staff ever since the forced consolidation of local hospitals and independent practices into large hospital systems in the late 1990s. It got worse in the early 2010s with many new CMS regs and a frozen payment schedule pretty much finishing off the independents. These issues have all gotten worse in the last two years due to the coronavirus. The first thing hospital systems did when patient numbers briefly dipped for two months in April and May 2020 were to cut staff (either fire them outright, lay them off, or cut hours) and cut benefits. The patient numbers more than rebounded last summer and have been very high since, and little to no staff have been hired to replace ones that were fired or quit, and pay/benefits for staff haven't budged for anything except absolute entry-level positions. Patients have gotten much more unruly for whatever reason or reasons and the hospital systems won't do much to protect their employees from this or back them up "because it's bad PR, the customer is always right." Add in the hassles of the coronavirus politics and mandates (particularly their employer twisting the school board's arms regarding restrictions and mandates for the schools their kids attend), and it adds up to too much for many and they quit. Apart from the VA, there is essentially no unionization of healthcare workers in this region so it's all individuals walking out and quitting and not an organized strike.
