Vi Editor is present in almost every Linux Unix system, even the most minimal.
It is very small. In fact, some versions have a total code size of less than 100KB. This makes it easy to include vi on even the tiniest versions of Linux, such as those in embedded systems and those that run from a single floppy disk.
Vi editor is typist-friendly, at least once you get used to it. For example, the commands are very short, usually just a few keystrokes. And because vi does not use the mouse, there is never any need to remove one's hands from the keyboard. This can speed up editing substantially.
Vi editor is very powerful, as just a few very short commands can make sweeping changes to large documents. In fact, vi is more powerful than most of its users realize, and few of them know more than just fraction of all the commands.