* Wage garnishment is limited, maybe the ruined the credit score and the max % of garnished monthly paycheck (%15) is less than what they are already paying?
* The type of majors and students background who graduated changed. Maybe universities 4 years ago decided to accept more students into majors which are having a hard time finding employment. Universities don't care, they just want more students with 6 figure approved loans to roll in.
* It is possibly there was a hint or signal of debt forgiveness being implemented. It doesn't have to be true, just a rumor but it can start to self-perpetuate because people really want to believe it.
* Also everyone is pretty connected these day via social media so maybe if someone bragged about not paying and "look a few months later, nothing happened to me" others might start thinking, hmm, well maybe it's ok. Certainly nobody wants to be left still paying like a fool if all their cool friend stopped and they still seem to be doing ok, kind of attitude.