I don't know much about corporations, but why business plans are needed at all? I mean, for EU citizens.

bank (loans), immigration and investors can be interested, but their interests are not covering every corporation out there.

It's basically a proof of "most basic effort" that you're serious. You could probably note down some stuff on a single A4 and get it approved, it doesn't have to be a 40 page dossier.

Kind of like fizzbuzz, just something really simple and most basic to get rid of the "easy scams" and so on.

Edit: So "easy scams" are probably the wrong word, I initially wrote "riffraff" because in my mothertoungue that isn't so... disparaging, but what I meant was that it's used as "bare minimum filter" basically.

There’s absolutely no need to have a business plan to start a company in Germany. You articles of incorporation and they state a company purpose, but this can be something as simple as “do IT consulting”.

Obviously, having a credible plan helps if you try to convince banks to loan you money or any such thing, but the act of registering a company requires no such thing.