That’s actually a fairly common misconception. Professors get fired for cause all the time with tenure. People can also be let go even without cause if the college’s board of directors votes to approve. Usually the board of directors won’t give individual professors any thought, but if the professor is acting in ways they believe go against the best interests of the school–even if it doesn’t strictly violate to the professor’s contract–boards can and do vote to let professors go in those cases.

Tenure exists to protect a professor’s freedom to research what they’re interested in, even if it’s not immediately fundable or a “hot topic.” It allows for faculty to stand up to deans when deans taking the college in a bad direction. It also allows professors to have the ability to require a constant level academic rigor to pass their class (e.g., even if a cohort of students is less prepared out of high school, they need to achieve the same level of mastery) since their contracts aren’t dependent on teaching evaluations–provided that the professors are teaching their classes as expected. Its only actual reason for existing is research freedom, though, and firing happens all the time for reasons unrelated to research.

Source: am professor