It just looks like student debt is correlated to population density[0] and inversely correlated to median income [1].

The difference between the delinquency map and average loan balance maps shows that people from places with low median income are taking lower loans but are still struggling to pay it back perhaps due to lack of jobs.

I do have concerns regarding the scale used.

[0] http://utahlandowners.com/wp-content/uploads/2015/03/MAP-U_S...

[1] https://upload.wikimedia.org/wikipedia/commons/9/9e/US_count...