For nurses on-call is a tiny amount - $3/hr and then you get 1.5x if you actually get called in
Software engineers are an interesting case; some have a great deal of domain-specific knowledge, giving them leverage over their employers. Many less so, and so a union could help. AI might change this equation too.
Replaceable with what, exactly? The local ER is now having to close in the evening because they can't find sufficient nursing staff to keep it operating.