Agreed. Why hasn't some male nurse sued over the inherent gender discrimination in the job title? We now have firefighters, letter carriers, flight attendants, chairpersons (or increasingly often, the simpler "chair"), but nurses are still called nurses.
They are only really called that in conversation. The official title (generally under contract) reflects their degree program: R.N., L.P.N., C.R.N.A., etc.