Because taxpayers are guaranteeing it. It’s how you get elected by both “helping” students and keeping taxes low.
Long term, you’re harming students and taxpayers, but short term the optics look like you helped and you don’t have a cash outlay for helping anyone so it doesn’t affect the budget.
Important note: defunding higher education also helps people get elected. It's been going for decades. My partner works for a state university system in a red a state and their budget has been cut every year since the 90's. People like to point at bloated administrative salaries and facilities when they talk about skyrocketing education costs, but the fact of the matter is that state schools receive a fraction of the funding they used to, and that makes for the majority of rising tuition costs.
Long term, you’re harming students and taxpayers, but short term the optics look like you helped and you don’t have a cash outlay for helping anyone so it doesn’t affect the budget.