Many good comments in this thread. I'll just leave a note of my experience and opinion.
I've used vim since about the year 2000. Before having access to a computer running a Unix, I'd read books about the Unix environment and fell a little in love with ed commands. Their power, yes, but also the immediacy of the user experience. It's just there, all the time, in vi.
Having coded a decent amount of vimscript... Eh. vim is not great (I'll likely never switch to neovim either.) Perhaps the best part about vim is the manual. There are so many features, some of which depend on/affect other features in various ways. I use vim for taking freeform notes, transcribing long form texts mostly - the auto formatting that can hard wrap at textwidth, without any extra command or keypress to trigger the formatting) is a feature I use a lot. The ability to quickly pipe text through Unix filters (mostly `par' in my case) is also great.
All this is easily done in emacs too, but I feel there's more immediacy in vi (and vimscript).
I salivate at the better unicode support in emacs, and the ability to have frames - separate GUI windows of the same emacs process. I would use these all the time. (g)vim likely won't get better in these areas within my lifetime.
Availability on mobile devices: I use an iPhone - it's from work, I have it with me all the time. I do not want to carry along any other device. A recent-enough version of vim is available in the AppStore as iVim. This has become the only note-taking app I can bear to use. It can write to text files on iCloud and access them later from other devices.
On vi clones - I wish Thomas Dickey's editor (vile) had become popular, instead of vim. Proper lexing and parsing for syntax highlighting (instead of regexp soup) - Imagine! I started out on computing with Red Hat Linux, where vim was installed by default - and most documentation, online resources, might have mentioned vim instead of any other clone, leading to vim gaining mindshare.