I think it’s because the software is generally simply considered part of the BOM and thus a cost to be reduced. Also, the hardware side typically rule the roost in such projects, and hardware engineers tend to look down on software developers because, after all, how hard is it to just type code in (if you’ve ever looked at code written by EEs…ugh).

As supporting evidence: the pay is better at companies that do take software seriously. Examples: at one class, Cisco; at another, FB, Google, Apple…