One reason I could think of is that as college education become more readily available for still more people, deciding not to go (gut feeling, isn't it really more often a decision not to go, rather than to go?) is a progressively more meaningful filter.
I'm sure a similar shift happened as high school became ubiquitous - then high school became a requirement for some jobs that were previously held by those with no high school.
This is generally a good thing, it's an artifact of society as a whole becoming better educated. The main problem with college is that it hasn't really caught up to it's new status as "general" education, rather than "elite" education. That said (I'm not american so not intimately familiar with the system), isn't it entirely possible to get a decent education (although with little "elite" signalling value, it would "tick the box" for college degree on the types of jobs the article refers to) from a state or community college and not have a lifetime of debt to deal with afterward?
It's popular to joke about how easy it is to get a college education in this state, but I don't think Georgia's $400+ billion GDP amid the century-long economic turmoil of this region is a coincidence. PINES probably helps, but I think Georgia's focus on getting everyone into some sort of college is key.
This is the key. I know so many people who insisted on going to an out of state of private school and now are deep in debt with poor job prospects and not many marketable skills, when they could have gotten the same education from a state school, and have poor job prospects and not many marketable skills but not be deep in debt.