That's something even President Obama occasionally pretends he doesn't know; in this year's State of the Union address he said:

Of course, it’s not enough for [the federal government] to increase student aid. We can’t just keep subsidizing skyrocketing tuition; we’ll run out of money. States also need to do their part, by making higher education a higher priority in their budgets. And colleges and universities have to do their part by working to keep costs down. [...] So let me put colleges and universities on notice: If you can’t stop tuition from going up, the funding you get from taxpayers will go down.
This is why you can't ignore Rush Limbaugh. Obama knows better, and on a press call not long after the State of the Union his Education Secretary, Arne Duncan, did emphasize the role of state funding in tuition increases. But the fact that the president, in his highest-profile address of the year, dispensed with state funding in a sentence and then focused on costs at colleges and universities, concluding with the flagrantly nonsensical "If you can't stop tuition from going up, the funding you get from taxpayers will go down," is a good sign of how broken the national discourse is. Because the data show that it's exactly when funding from taxpayers goes down that tuition goes up. Quality education doesn't get cheaper because funding gets cut—instead, either quality declines or tuition goes up.

Oh, but what about waste? What about unreasonably high salaries? There is some of that. But it's to be found among exactly the people who would be tasked with making decisions about how to cut costs within a given college or university: administrators. For 12 straight years leading up to 2009, senior administrator pay rose by more than the rate of inflation. Their ranks grew, as well:

...from 1976 to 2005, the number of full-time college administrators (vice presidents and deans, for example), rose by 101 percent, while the number of full-time nonfaculty professionals (in student services, development, and information technology, for example) rose by 281 percent.
Over the same period, the number of full-time tenured and tenure-track faculty members rose by only 17 percent.
Cost savings at colleges are decided on by the rapidly growing ranks of well-paid administrators, and the costs cut tend to be among faculty, the people who actually teach students. That work is increasingly being transferred to low-paid adjunct professors. Not only is the low pay adjuncts face an issue in itself—to pay the bills, they may forced to teach more classes than is good for them or their students—but it goes along with factors that very directly affect students:
For example, adjunct faculty often have trouble connecting with students because they lack office space, and thus can’t mentor struggling students. Their fragile position as contract workers also means they are less able to be outspoken about campus reform and improvements, and less able to advocate for their students when administrative issues arise.
Studies have indeed found both that high numbers of adjuncts, and especially adjuncts with poor working conditions, have adverse effects on students. To be clear, this is a systemic problem, not a problem with the individual teachers. But the issue, when we're talking about higher education funding and tuition, is that this is exactly the cost-cutting measure that administrators tend to turn to—they're sure as hell not cutting their own jobs.

The miserable wages and working conditions faced by adjunct professors, and the fact that there are so many adjuncts because good college teaching jobs haven't kept pace with the number of students needing to be taught, aren't the only ways rising college tuitions and student loan debt are a part of the broader war on workers. Putting people into the catch-22 of a college degree being a virtual necessity for a middle-class life but one that requires students who don't start off middle class to accumulate large debts helps keep people trapped, struggling not to fall further behind rather than figuring out how to change the system. If we make higher education—the kind middle-class kids have gotten all along, not something with the same name but lacking big parts of the actual education—available to anyone who wants it, without a lifetime of debt, suddenly the economic prospects of the coming generations start looking really different. The fact that instead, investment in college students is going down? That's not an accident.