It might also be cheaper to use cash, given banking isn't typically free in Germany.
It eliminates a multitude of steps (sign up, proof of identity, credential management) to accessing any government service from booking COVID tests to paying taxes.
Although I wouldn't be surprised if the prolonged use of the DigID app (i.e. because it keeps crashing, or is offline for maintenance again) would have caused maniacal insanity.
Edit: The app works most of the time, but it is very unstable and not at all user friendly. No QR-code scanning feature but manual code input only, no login confirmation, no active session management or insight, most services allow you to log in with just your username/password and don't require the app at all, etc.
I do wonder why that code has to be manual and not embedded into the QR code, I assume there's some reason for it. But it's also only four letters, not terribly tedious.