The short version: "A major factor driving increasing costs is the constant expansion of university administration."
I think that in many cases universities have turned to hiring staff to circumvent many of the political problems of trying to manage professors (edit: tenured people are a bitch to manage and will resist any and all changes in most departments, in case this wasn't clear before). It's a poor solution but in some areas it's the only way to make changes.
The IT, the slow rate of change among faculty, the part-timers, etc, could optimistically be put down to changing student and market demands. Pessimistically much of it could be put down to an institutional desire to have central control.
The story has been related to me like this: Traditionally universities were heavily influenced by the faculty, who had big sway over big decisions. This all came to a head in the 80s when faculty and the administration disagreed over some big issue (like who should be the next president, I believe). The faculty and administration went to court, and the court ruled that the faculty were employees and the administration, essentially, had absolute power and could appoint who they wanted.
This precedent drastically changed how universities were run, and since then faculty has basically been eviscerated (both from a power standpoint and a pay standpoint, ala adjuncts) and universities are now run like businesses (top down management vs. a more distributed/democratic form previously). I haven't been able to find the court case or citations to back this up (closest is a book[1]), but it wouldn't surprise me if true. It would explain a lot that has happened, and if you combine it with other factors like government backed student loans, it's no surprise universities are cash cows run by feudal lords.
On the research side, off the top of my head you've got grant administrators, institute review boards, research integrity office, postdoc affairs. You've also got "Title IX administrators". Accepting federal funding takes a lot of work.
The worthiness of the services the bureaucrats are providing I leave as an exercise to the reader, but I think it's problematic that the people making the regulations are not the ones paying the bills when it comes time to comply with the regulations.