Climbing walls, Jacuzzis, exotic chefs. There are lots of (misguided) explanations for skyrocketing tuition costs at public colleges and universities, which educate about three-quarters of America’s postsecondary students.

Of course, very few schools actually offer any of these country-club-like amenities, despite the attention and mockery they’ve earned in the press. So on to the latest scapegoat: greedy executives, or so suggests the coverage of two recent reports about highly paid college presidents. Their outsize compensation is supposedly yet another sign of bloated, bureaucratic colleges’ inability to control runaway spending.

You can definitely debate whether public institutions are spending on the right things (including compensation for both executive and athletic personnel; in most states, the highest-paid public employee is a college athletic coach). But these days it’s hard to complain that public colleges are spending too much overall, or even that their spending is rising. Total spending per student at public schools has actually stayed about flat over the past decade, once you control for inflation.

So why, then, is tuition climbing so quickly at public schools?

The biggest driver isn’t lavish rec centers or fat-cat presidents or overstaffed career counseling centers. It’s politicians: State legislators have shifted the burden of paying for college away from taxpayers and onto the shoulders of students. Public colleges have gone from being “state-funded” to “state-supported,” and now, finally, just “state-located,” as one university president quipped.

Over the past five years, educational appropriations per full-time-equivalent student have fallen by nearly a quarter, according to a recent State Higher Education Executive Officers report. Faced with declining public subsidies, schools have been forced to raise tuition dramatically. Even those tuition hikes, though, have not fully offset public funding cuts: Appropriations have fallen by about $1,800 per student over that time, while net tuition revenues have increased by “only” $1,100. Schools have dealt with the funding shortfalls by different means, including increasing class sizes; shifting more of their teaching loads onto poorly paid adjuncts; deferring maintenance and repairs; and, in some cases, restricting enrollment in the disciplines that are most expensive to teach (even though disciplines that are resource-intensive, such as nursing, often happen to be the ones that offer better job prospects). Some of these changes, you’ll note, suggest that students are paying more but getting less. (The same may not be true of private schools, which are also raising tuition sharply but adding lots of staff.)

State legislators have been paring back higher ed funding for a few reasons. One is obviously the financial crisis, which led to steep drops in tax revenues. But the declines in college subsidies are actually part of a trend that long predates the Great Recession.

Over time, mandatory spending on things like prisons, pensions and health care has crowded out discretionary funding for higher ed, even as college enrollment has swelled and as postsecondary credentials have become an increasingly common prerequisite for getting a job.

“If you’re a state legislator, you look at all your state’s programs and you say, ‘Well, we can’t make prisoners pay, but we can make college students pay,’ ” Ronald Ehrenberg, the director of the Cornell Higher Education Research Institute and a trustee of the State University of New York System, once told me in an interview.

State budget cuts also seem to reflect changing public attitudes toward higher education.

From the days of Benjamin Franklin, through the foundation of land-grant colleges during the Civil War, and then up until quite recently, higher education (just like primary or secondary education) was seen as a sort of public good: a service whose benefits were shared among the entire population and whose costs should therefore be borne by the entire population.

This makes sense. Yes, most of the perks of higher ed likely accrue to the individual who gets the degree. But college-going also has huge spillover effects for the rest of the economy. Research by Enrico Moretti, an economist at the University of California at Berkeley, shows that having a greater density of college grads raises everyone’s wages — especially, in fact, the wages of workers without degrees. College is also one of the best tools we have for promoting upward economic mobility among the poor, as research by Pew’s Economic Mobility Project has demonstrated.

Which is exactly why shifting the burden of college costs away from taxpayers and onto students is so shortsighted. It means that attending college, or more important, the prospect of actually graduating , is stretching further out of the reach of the workers who need to upgrade their skills most — and whose skills the country’s future depends on.