Research software engineers are paid what they are worth. Typically a bit more than a postdoc, but not that much more. The problem is that the academia is a cash-starved environment, and everyone's work is worth much less than similar work in the industry.

Another problem is the PI-centric model. Most of the funding goes to individual labs. If a typical grant is $200k/year, you are not going to pay competitive salaries. And you're probably not going to hire a software engineer, because then you won't have anyone doing the actual research.