In the case of the University of California system, it's almost 1:1 substitution, declines in per-student funding being matched by increases in tuition. Partly due to actual cuts to the UC budget since 2000, and partly due to funding not keeping up with increases in student numbers. The state government mandates these increases in student numbers, but in recent years has not been willing to fund accordingly.
The mandate is that the UC system is required to offer spots for the top 12.5% of the current year's in-state graduating high school seniors, so this mandate obviously expands if university-age population increases. Which to be fair is sensible: it makes sense for the state university system's size to be roughly proportional to the size of the state's university-aged population. But then you should fund it proportionally too.
Which is not to say overpaid administrators aren't also sucking out more money than they should be. The UC Office of the President (UCOP) is currently being deservedly raked over the coals by the state auditor, and I would not shed a tear if UCOP's budget specifically were cut. But in terms of big-picture trends, the state's per-student funding declining from $30k/student in the '70s and '80s to less than half of that in 2012 is a pretty good first-order explanation.
The mandate is that the UC system is required to offer spots for the top 12.5% of the current year's in-state graduating high school seniors, so this mandate obviously expands if university-age population increases. Which to be fair is sensible: it makes sense for the state university system's size to be roughly proportional to the size of the state's university-aged population. But then you should fund it proportionally too.
Here are some numbers I put together a few years ago (not updated since 2012): http://www.kmjn.org/misc/uc_funding.txt
Which is not to say overpaid administrators aren't also sucking out more money than they should be. The UC Office of the President (UCOP) is currently being deservedly raked over the coals by the state auditor, and I would not shed a tear if UCOP's budget specifically were cut. But in terms of big-picture trends, the state's per-student funding declining from $30k/student in the '70s and '80s to less than half of that in 2012 is a pretty good first-order explanation.