The aquatic center at the Cary Street Gym includes two swimming pools, a slide, and a second climbing wall. - 

So the average price of a four-year college has more than doubled in the last 30 years -- that's what the College Board tells us. And -- in part, because of that -- the average student graduates with around $25,000 in student loan debt. All this is becoming a pretty familiar story.

But what's often missing from the discussion is WHY. Why is the price of higher education rising so much faster even than health care? Marketplace's education correspondent Amy Scott investigated a growing trend of lavish student gyms and dorms and whether it contributed to the rising cost of tuition.

While "zero-entry" pools and high-end dormitory dining get a lot of attention, tuition hikes mainly stem from declines in state funding for higher education, as well as rising health care costs and financial aid.

Ironically enough, "there's even sort of a disincentive to lower prices, because there's a sense that if a college charges a lot, it must be good," Scott said.

Learn more about how college tuitions have increased so much by listening to the audio above.

CORRECTION: An earlier version of the summary of this interview incorrectly described the primary reasons behind rising college tuition. The text has been corrected.

Follow Amy Scott at @amyreports