The more people you let through any conduit to success, the less each will be worth.
When women started working, doubling the work force, salaries effectively declined with the value of currency.
Now that we're handing just about anyone a college degree, having a college degree isn't a big deal anymore -- and so it doesn't translate to salary.
There is no magic point at which a genuine college-level education becomes an option, but anything below an IQ of 110 is problematic. If you want to do well, you should have an IQ of 115 or higher. Put another way, it makes sense for only about 15% of the population, 25% if one stretches it, to get a college education. And yet more than 45% of recent high school graduates enroll in four-year colleges. Adjust that percentage to account for high-school dropouts, and more than 40% of all persons in their late teens are trying to go to a four-year college--enough people to absorb everyone down through an IQ of 104.
There's no point going to a college that someone with an IQ of 104 can pass -- it's high school II (if even that; more like High School 1.5).
Now that 40% of the population goes to college, instead of 15%, a college degree is that much less valuable, and employers are noting this.
But we all had to be egalitarian and cram everybody through college that we could, because it's the "right thing to do," even though it meant dumbing college work down and devaluing the college degree.