Drop out vs. flunk out are very different. The flunk out rate has to be minuscule (i.e 1-2% max and even that feels high). At my school if someone is really struggling academically they usually just drop them back to redo a year. You’d have to fail again then to probably even be considered for dismissal.
Voluntary withdrawal due to either change of heart or some other extenuating circumstance - while rare (of my class of 140 I think this applies to 3 or 4 people) is much more common than actual flunking out. It usually happens during/ right after 1st year. I imagine dropping out later than that is extremely rare.