Here's the thing...
Student loans exist to make the gov money, they see it as a form of enhanced taxation. College tuition has been rising, and so have student loans. The government's answer has been to throw more money into loans and do nothing about the problem of the massive and exponential increases in the cost of higher education.
When you start grad school you get hit with the biggest burden with rates at 6.0%+ (my first year was 6.8%) and grad plus loans to cover the rest to the tune of rates beyond 7% (my first year was 7.9%).
The average student in a professional program is going to borrow 150k+ per year, with that number growing increasingly. The system is set up to screw over graduate students and hit them with big bills to fund the gov and essentially subsidize the loans of those who overspent to get a cruddy undergrad degree.
Higher income earners like physicians, pharmacists, lawyers, etc require professional doctoral education to the tune of hundreds of thousands of dollars in cost. The wages are over six-figures. Tax deductions on student loan interest ends once you make more than roughly 75k. The system is set up to where not only do you pay higher federal income taxes due to higher wages, but you'll also have a higher debt burden and more interest profit the government makes on higher earning individuals after school. It's a double whammy with the taxes and the loans. Democrats did nothing to fix it, Republicans don't have a viable plan. In the long run you make more than peers, but the amount of wealth you get to keep for yourself and your prosperity are taken from the gov because you have the money to take. They really don't care, it makes them a killing to farm out grad students who can afford to make higher payments. It's corrupt and wrong. I highly doubt Sanders would do anything substantial about it, Obama didn't (and arguably made things worse) and their focus seems to be on the fools that spent 100k+ to get worthless bachelor's degrees from overpriced preppy schools who can't afford their debt bill waiting tables or making coffee at Starbucks.
