It crops up over and over. If X is a path to upper-middle class or above, it's almost inevitable that filters and gates are put in to place that primarily work to ensure it's available only to children of the upper-middle class or above.
There's nothing inherently within most software development that makes it out of reach of being treated like a technical skill like electricians, carpentry, or plumbing.
Personally, I suspect it's more to do with "cultural fit" issues than skill issues. College is a great filter to find people who self-select and are trained to fit into the global corporate world.
Unfortunately, the side effect of this is concentrating wealth into the hands of people whom already have significant wealth and advantages. Efforts to counteract this (like the GI Bill, and college loans) have tended to have additional expensive barriers to weed out people deemed a "bad fit". For example, requiring more advanced degrees or hard to get internships (that may even be unpaid!).