That's the difference between discretionary spending and mandatory spending.

Discretionary spending largely aligns with what the organization is supposed to do. A university can choose how much effort it puts on educating the students, because education is discretionary. Mandatory spending, on the other hand, is what the organization must do, due to external reasons or earlier commitments. Because mandatory spending is beyond the direct control of the organization, it tends to bloat.

The biggest sources of administrative bloat seem to be regulations, student expectations, and running a residential campus. None of which are particularly easy to change.