But those unions are negotiating against employers who have immense market power. State governments essentially have the last word on teachers’ salaries, and a lot of the country has consolidated to the point where there are only 1-3 major hospital networks in any area.
Without the ability to switch employers for better pay, the unions are the only way that those professions have to improve their pay and working conditions. (This may explain why travel nurses get much better pay than most nurses.)