> It's difficult for me to imagine what it would take to get a doctoral thesis revoked.

Personal grudges. Academia is full of them.

Different leadership.

If some in your experience erred on the side of leniency, then it stands to reason that others might err just as egregiously in the opposite direction.

In fact, your anecdote suggests erring is the norm. We should thus expect punishments to be inappropriate in one direction or another. An appropriate punishment seems rather unlikely.