This 100%Speaking as a former nurse, there's definitely an element of seeing it as "women's work" and expecting therefore that's its really just cheap labour and what are they upset about.
If nursing was (or traditionally had been) dominated by men but required the same degree, years of ongoing medical training, the unsocial hours and pure physicality I guarantee it'd pay 3 times what it does.
Although medicine, traditionally male dominated although no longer, is going the same way, with consultant pay falling in real terms by 20% over the last 10 years.