vim has better default keybindings/commands that allow for less movement of your hands. Nowadays, in reasonably current versions of nano, that's mostly it. The main difference is nano is somewhat usable but extremely inefficient unless you learn it, while vim forces you to learn it to get anything done at all, which also pushes people to spend a bit of time learning it in general.
If you're sure of the numbers you're using, vim's ability to repeat commands is also helpful. In practice I find that it's really hard to make use of them beyond low numbers, where nano can still achieve things in similar amounts of keypresses. Eg something to delete 3 words like <escape>3dwi can be done similar with a sequence like Alt-A ^→ ^→ ^→ ^K in nano. Make it 20 words and nano is going to be a lot slower, but that's quite an uncommon action.
But the practice is that nano users don't spend time learning any of that and just hold delete until the words are gone, which takes forever. Everyone that can do basics in vim quickly learns that you can dw words away and make it 3dw to delete 3 of them. The default, easiest to use & access tool for any given situation gets blamed not just for its flaws, but also for the users that don't want to spend time learning any tool.