You have to be careful with conflating causality. As we turn college more and more into highschool 2.0, we're going to see the correlation with increased earnings start to deteriorate. There's a simple matter that we're greatly increasing the supply of college educated individuals which, in turn, will have a diminishing effect on their demand which will drive earnings down. The only way this will not happen is if there's a proportional (which is to say sharp) increase in the number of available and desirable positions for college educated individuals.
This is also ignoring that we've greatly widened the demographic attending colleges. The reduced selectivity means that the average person is not going to be as top-notch as they were at one time, which means that the average expectation of an individual with a college degree will also go down. This will also have an aggregate depressing effect on our earning:education correlation. More important than ever will become median earnings for college graduates. The top graduates are earning vastly more than ever before which will mask the overall problem.
This is also ignoring that we've greatly widened the demographic attending colleges. The reduced selectivity means that the average person is not going to be as top-notch as they were at one time, which means that the average expectation of an individual with a college degree will also go down. This will also have an aggregate depressing effect on our earning:education correlation. More important than ever will become median earnings for college graduates. The top graduates are earning vastly more than ever before which will mask the overall problem.