You don't think software development itself is a highly specialized skill? It's true that what we type might not be PhD research, but just learning a programming language is a rare thing.
It certainly takes less schooling than doctor or lawyer. Admittedly part of that might be that there are things we can work on of less consequence as we figure things out, so we need a little less prep for a exercising comparably specialized skill. Of course, part of the pay discrepancy is also going to be covering the difference in schooling costs = who spends longer paying off student loans, on average?
Part of that schooling involves intense preparation for tests put forth by the state before you are even legally allowed to perform the work you've been studying for.