My personal theory on how Super Monkey became Yoshi's Island:
Began as a Stanley game with DK and a monkey army as the villains, Rare pitched DKC, it was approved, having DK as the antagonist would be contradictory when a game starring DK as the hero is coming out at the same time, so instead of creating a new set of antagonists for Stanley to fight the game was reworked into a Yoshi game featuring existing Mario villains, and eventually evolved into something completely new.
Don't take this as fact, just my theory.
Began as a Stanley game with DK and a monkey army as the villains, Rare pitched DKC, it was approved, having DK as the antagonist would be contradictory when a game starring DK as the hero is coming out at the same time, so instead of creating a new set of antagonists for Stanley to fight the game was reworked into a Yoshi game featuring existing Mario villains, and eventually evolved into something completely new.
Don't take this as fact, just my theory.
Some tales
Are better left untold