It's not so much about poking fun at him as an individual. I'm sure there are nice things about Lösch as well as dislikable things about Franz. We're all a mix of good and bad.
He is, however, a figure in a position of high authority over several million people and, along with his close colleagues, is responsible for manipulating* and being, shall we say, less than honest with them on certain matters. As with any figures of authority (governmental, corporate, religious) who are party to hypocrisy and promoting untruths, he is fair game for parodying.
Nevertheless, if it was somebody I knew and liked personally who was being lampooned, I would probably be defensive too.
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* E.g. likening going on to Higher Education to putting a loaded gun to your head and pulling the trigger - the person might survive the gunshot and the person might survive College but neither course of action can be recommended.