I’m skeptical of the narrative that trades is some great career choice, but "Well if you aren't in one of the good areas you'll get fucked" applies to pretty much every career choice.
Ah, the social mobility of the american dream.
In a poorer society equivalent menial labor is more poorly paid than in a richer society. Edit to add: And in a poorer society some of the highly paid menial labor that exists in richer societies may just not exist, or at least not in the same amount.
All the other stuff like expertise and value is, counterintuitively, near irrelevant. For instance postdocs are some of the most highly educated and ostensibly highly skilled individuals - and many have taken on hundreds of thousands of dollars in debt to get to where they are, yet they earn about as much as a plumber does, because there's far more supply of postdocs than there are jobs/positions for them.
So putting all the theory into practice. There are usually three possible reasons. Supply is too high = excessively high rates of software training/education. Demand is too low = not many roles for software developers. Or the companies that are hiring aren't making much themselves so the "maximum affordable cost" is relatively low.