It breaks about every convention on editors and discoverability that you're used to.

Start GNU nano. It puts me in a position where typing edits the file I opened. It shows me the name of the program. It shows some keyboard shortcuts for interacting with the program. (Though for beginners the ^X syntax isn't obvious either).

Vim, doesn't give me any of that. I infrequently use vim and I still tend to open a file and start typing without hitting i first, because it's behaviour that's inconsistent with every single other editor I have ever used.