In the case of the two governors, the parents could certainly have taken higher paying jobs and been able to pay OOP. They chose a lifestyle and their kids have to live within that income too. If they don’t want to say no to their kids, they should choose a different job.
It is one thing to borrow $10k extra which the parent knows can be paid back quickly, entirely another to borrow $300k and intend to keep borrowing for more kids with no change in income. The issue could be tamed with limiting the amount of a PLUS loan or limiting the amount the government will guarantee for a private loan.