Why does evil create new functions instead of making key bindings for those already existing?

I looked up the function for the keystroke C-p and it is "previous-line". And the function for the evil key "k" is "evil-previous-visual-line". Why to make functions for the stuff already available? why not make your keybindings attach to existing functions?

Because Evil implements Vim and the movement command in Vim behaves slightly different from the one in Emacs: ;; The purpose of this function is to provide line motions which ;; preserve the column. This is how `previous-line' and `next-line' ;; work, but unfortunately the behaviour is hard-coded: if and only if ;; the last command was `previous-line' or `next-line', the column is ;; preserved. Furthermore, in contrast to Vim, when we cannot go ;; further, those motions move point to the beginning resp. the end of ;; the line (we never want point to leave its column). The code here ;; comes from simple.el, and I hope it will work in future.