I've often posited among friends in the industry that it's partly due to apathy and mismatched expectations. College students go into CS because they expect a good paying job, not because of any specific aptitude or interest. CS isn't the study of software engineering, nor of the act of programming. They graduate, with no appreciable skill, and no real desire to learn, and can't find work. We can argue about fairness until we're blue in the face, but the reality of the situation is that motivated students who are actually interested in learning have vast free resources available to them to learn and free resources available to them to demonstrate their competence. Anyone not taking advantage of these resources is going to be subpar compared to others in the labor market.
Pretty much anyone who went to college in the last 20 years should have been able to anecdotally identify the stand-outs in their classes, and in general on the other side of the pipeline those are the only folks having an easy time getting hired. I dropped out of college, even though I was one of the stand-outs, because I wasn't learning anything I hadn't already taught myself. I've had less difficulty in my career than some of my former classmates I keep up with and my salary is multiples of theirs when they are employed, we're all the same age and they're technically more credentialed. It comes down to the fact that most people are just not very good at programming or at systems design. In fact, I'm not a good programmer, my skill-set is very much in the arena of systems design.