I'm not quite sure how it is ever expected that they do. The fees for tuition in the US are extortionate, there's little hope for most ordinary people to pay them back. Only those people who go on to have elite professions will be in a position to do so. Mortgage debt is largely different because there's at least a house as collateral, if too many people default on their payments then house prices will crash, but it's better than in the case of student debt where there is nothing to lay claim to.