The reason they're under-compensated is that they aren't valued, unfortunately. A lot of scientists are self taught programmers and don't know what they don't know. The other issue is that if you say you should spend half your departments budget on hiring much better paid software developers, it looks really bad:

a. You're implying your colleagues are incompetent.

b. You can't use that money for "science".

c. It puts in painful relief that the software guys are much better paid than you are, implying that their work is more valuable than yours. But a lot of scientists put up with low pay because they believe their work is really valuable.