By far and away the biggest abuses are allowing PhDs autonomous control of their careers. And once given tenure, they simply take those bad decisions and put them in affect for life. We have faculty that do not teach, do not write grants, do not do research, or take on administrative appointments to act like they are busy. Some have not been on campus or in the same state for months or years at a time. All the while, they draw salary because they are tenured. Those that retire milk the system for a huge retirement bonus, then get rehired; only death will get them to leave and make room for another generation. They let students fail and retake classes, allow students to take up to a decade to earn their PhDs, even allow students to live in other states while earning their degree.
The problem is "peer-review" management. They are their own bosses, they make their own decisions and once given tenure have absolutely no accountability to anyone but themselves. Fail.