Of course everyone involved knows they will face consequences, but they may feel those consequences are better than the payments. Courts can’t garnish paychecks that don’t exist and a ruined credit rating only matters if you were ever going to be able to afford to buy a house or car in the first place. Afaik actual jail time isn’t really a thing for defaulting on a loan. If the only leverage the government has to get people to pay the loan is to threaten their future financial security, then anyone who thinks the initial promises of security is bogus has nothing to lose.
There’s also some people who are willing to take the hit just to send a political message.
That said, I suspect nowhere near 62% of borrowers will actually meaningfully boycott in any way.