Once upon a time, a university was a collection of scholars who decided to do some ancillary activities in concert. The dons/scholars/professors made group decisions and some few of their number sacrificed themselves administering those ancillary activities part-time. Those days are long gone, at least in the US.
Recent decades have seen rampant growth in administrative overhead, and a corresponding diminution in the ranks of tenure track faculty. DEI hires made this trend worse. "Tenure track" includes both tenured faculty and those in junior positions where one is must either get promoted and earn tenure or leave.
Of course, when there are fewer tenure track faculty, the classes they would have taught are taught by the non-tenure track instructional staff, variously called adjuncts, instructors, visitors, locums, teaching fellows, contract faculty, and part-timers.
These often don't know from term to term if they'll be reemployed. Typically, gig faculty teach lower division introductory and general education courses and supervise labs. They aren't paid especially well and many part-timers don't get health insurance.
Some campuses have experimented with giving faculty 5 year renewable contracts in lieu of tenure. The renewal decision comes in the fourth year so someone not renewed has time to make future arrangements while still employed.
Today I saw an article in the RealClearPolicy list with this title: "Tenure Track in Higher Ed Is Going Extinct," published in The American Mind, a Claremont Institute publication. Assuming the trend line doesn't reach an inflection point, the predicted extinction is a distinct possibility.
Personally, I have mixed feelings about tenure. I had it, was glad I did, and relied upon it to keep my job open while I took a couple of leaves to do "growth" things. Yet I saw examples of the harm it can do to both students and the institution.
In the business school faculty (n = 50+) from which I retired we had one tenured faculty member who spent an inordinate amount of class time obsessing about nuclear disarmament and another who routinely told his students they were pathetic losers who would amount to nothing.
We never succeeded in getting rid of either, although we tried. A couple more were not quite as bad, but most of us did our jobs acceptably and behaved. The ratio was similar in the other DrC's college.
I have to admit the ratio was even worse among administrators. They could be fired, and some were. I remember a woman dean who was a drunk, and a Vice President who sexually harassed female staff. Both moved on eventually, possibly under threat but not actually fired.