Why is vi so popular?

IMHO, the reason vi has outlasted almost every other editor out there is because of its ability to work in almost any environment.  Almost all other editors require either graphical environment or curses (including emacs, pico, nano, etc).  Plus, vi has grown in capability over the years so many of the features available in other IDEs or editors are available in some form in vi.  If you can't tell, I'm one of "those" people that tell other unix/linux users that they should at least learn to use vi even if they prefer another option because you know it will be there when other editors fail.  As an example of vi adaptability in all environments, I've even had the pleasure of using systems that have no arrow keys, so the hjkl navigation keys made it possible to get around.  In an even more extreme case, I had a headless box that was connected to a line printer so I had to use vi in ex mode to edit a file.  Can't speak for anyone else but that's why I tell everyone they should at least learn vi.

All of that said, I do actually prefer vi.  Even though I mostly manage right now, I still do a fair share of development work and I use vi for just about every language I code in.  I have relented in the case of Java where I fire up Eclipse for any major project but for quick edits, I still fall back to vi.  I can still probably do complicated global search and replace tasks using regex faster than most can with the search and replace functions in most IDEs.  I find myself typing "jjjj" and <esc> in Word sometimes when I'm not paying attention.

IMHO, the reason vi has outlasted almost every other editor out there is because of its ability to work in almost any environment.  Almost all other editors require either graphical environment or curses (including emacs, pico, nano, etc).  Plus, vi has grown in capability over the years so many of the features available in other IDEs or editors are available in some form in vi.  If you can't tell, I'm one of "those" people that tell other unix/linux users that they should at least learn to use vi even if they prefer another option because you know it will be there when other editors fail.  As an example of vi adaptability in all environments, I've even had the pleasure of using systems that have no arrow keys, so the hjkl navigation keys made it possible to get around.  In an even more extreme case, I had a headless box that was connected to a line printer so I had to use vi in ex mode to edit a file.  Can't speak for anyone else but that's why I tell everyone they should at least learn vi.

All of that said, I do actually prefer vi.  Even though I mostly manage right now, I still do a fair share of development work and I use vi for just about every language I code in.  I have relented in the case of Java where I fire up Eclipse for any major project but for quick edits, I still fall back to vi.  I can still probably do complicated global search and replace tasks using regex faster than most can with the search and replace functions in most IDEs.  I find myself typing "jjjj" and <esc> in Word sometimes when I'm not paying attention.