They're doing them with relatively low paying jobs and as a result they're doing it through good old fashioned savings. Note that I think this is important because it builds character and sets them on a life long goal of thriftiness. It teaches them to conquer their problems head on right out school and to be creative about how to do it. It should become and has started to become a right of passage for many young Americans.
Think about this. Here's an article about a young woman who was able to pay off a huge chunk of debt in a short time with relatively low paying jobs. When somebody proves that they can do this, then it opens up a whole new world of living that sets them on a trajectory of doing great things! Down payment for a house? No problem! Need to save for retirement? Chump change! Emergency fund? Overseas vacation? I got that!
Consider it practice for life. The average student loan debt in this country is a little under $30,000. Which is only a few grand more than the average auto loan. And yet nobody seems to have a problem with paying off their car in 5-6 years max!
A great read that should be for all college students is the book WALDEN ON WHEELS. I'm commented on it in the past, but it's worth reviewing because this recent grad went through hell and high water to pay off his enormous student debt in record time. He will admit to you that he's a stronger man for it.