Why would someone use joe?
It uses WordStar key bindings by default. This was a common word processor in the early 80s, and I even used it in the early 90s. And perhaps even more relevant to a tech crowd, these key bindings were taken up by Borland's popular IDE for Turbo Pascal and Turbo C.
When I first got into Linux, I looked around for an editor that made sense to me, and hey, there it was.
I imagine that some other now-skilled Unix/Linux users followed the same path, because Linux arrived just at the end of WordStar's effective life (not to mention Borland's). So, one of the reasons is simply "timing".
Modern versions have syntax highlighting and other fancy features, so I haven't bothered to switch away.
(I know how to use vim for editing config files, though. That's kind of a mandatory skill.)
It's easier to learn than Vi, faster to start than Emacs, and more powerful than Pico/Nano (e.g. it has ctags support for programming).
But it's unlikely to be installed everywhere, so you should still know the basics of Vi and Emacs.
I use joe in its "jstar" (most WordStar-like) configuration.
Since I'm not a programmer or system administrator, I don't have to worry about whether joe is installed on any system set up by anyone else.
If someone else in my family has to type something on a system of mine, I can set them up with joe. It's the only *nix editor with a humane interface.
See how a nine-year-old reacts to such an interface: http://www.wordstar.org/index.php/wsdos-documentation/131-the-emperor-s-new-clothes-or-how-difficult-is-it-to-learn-the-wordstar-keyboard-commands
Joe was included with every early Linux system I used. (I started in 1994, when I changed jobs and was given an account on what I was told was a "BBS" on a "Unix" system at work. It was probably Slackware, and like all or most early distros, it included joe by default.)
I view using joe as a matter of principle. I started with WordStar in 1982, and soon learned that its command keystrokes are all part of the most basic standard of computing -- ASCII (a.k.a. ECMA-6 and ISO 646:1991 IRV), which we all still use in the extended form called Unicode.
Just Ctrl-A through Ctrl-Z are more than enough for cursor and screen control, basic editing, and operation of a full-feature menu system. They employ the keys we are most familiar with; where Ctrl is above left Shift, they can be typed as easily as capital letters; and with systematic assignments and as-you-work on-screen help like WordStar's (joe's is almost as good), they can be used immediately and internalized effortessly.
And because they are part of a standard and available on all systems, powerful companies want them to die.
Apple wants us to use only the Command key. IBM and its adherents and imitators want us to think that Alt, function, and dedicated movement and editing keys are indispensable. Look at mass-market software other than WordStar from 1982 to 1992: in Word, WordPerfect, Windows 1.0-3.0, and every other big-name product I saw, Ctrl-A through Ctrl-Z were all or mostly dead as a doornail. Look at product reviews from that time: even writers who loved WordStar seemed required to call its command keystrokes "arcane" or "cryptic."
How can something shown by default on your screen and explained clearly in the manual be called arcane or cryptic? The consistency with which those words were used is striking. I have been a professional translator, editor, ad copywriter, and technical writer, and it would never occur to me to use those particular words, even for a program that I hated. I can't shake the feeling that they were chosen in a boardroom or marketing department.
I swore long ago not to let any hardware or software company make me its slave. When forced to use WordPerfect and Word at work, I WordStarized them to the hilt, and at home I went straight from WordStar in MS/PC DOS to joe in GNU/Linux.
I appreciate the beauty of vi/vim and the power of emacs, and I'm happy to use their typing-zone command keystrokes in bash, browsers, window managers, and elsewhere. For working on text, however, I find that only joe meets my needs and requirements, and I expect to use it until I can no longer set finger to keyboard.
"WordStar... was a triumph of both software engineering and what we would nowadays call user-centered design." -- Matthew G. Kirschenbaum, in Track Changes: A Literary History of Word Processing