In addition to large amounts of new construction, administrative staff has expanded massively [0].

Between 1975 and 2011, the number of full-time, tenured faculty at universities grew by 23%. The number of administrators grew by 369%. The trend seems to be to hire part-time and untenured faculty to keep salaries down, then hire more administrators.

[0]: See "Full-Time Nonfaculty Professional" at https://www.aaup.org/sites/default/files/files/2014%20salary...