Or just some variant of "time for a change and this opportunity came along." Which whether or not it's the case with you, holds true for a lot of people who have been at a place for a while.

>The goal should be for you to part on good terms, not to take a last shot at them, which will only make them hate you.

Absolutely. Any satisfaction from bomb tossing in an exit interview or twitter thread is short-lived and the consequences may not be.