It's not a comment on quality or usefulness, and only indirectly its resource consumption (vi/vim consumes less than emacs in its default configuration), it's really about standards.

vi and the ex editor language are part of the POSIX standard and were around early in the history of BSD. See the history here: https://en.m.wikipedia.org/wiki/Vi

For a well worn joke on the subject, "Ed is the standard!": https://www.gnu.org/fun/jokes/ed-msg.en.html