"the shell" usually means (on modern Linux distros) bash, which is the "GNU Bourne-Again SHell".[0]
Brian Fox[1] developed the readline library to handle bash's interactive input. Between Brian Fox having been an Emacs maintainer, and bash being a GNU project, the keybindings followed suit...
Had bash been "Bill Joy's[2] Awesome SHell," things might have gone differently :-) Well, it would've just been csh[3] (written by Bill Joy.)
[0] I address this introduction to anyone not already "in the know."
Actually the keybindings can be changed to those of vim (by typing "set -o vi" on terminal). It is probably not set as default as it is confusing to new users.
(btw, if you learn emacs well enough, you're commandline-fu goes through the roof)