Some degree of stability in seeds is desirable, partly because of the compatitive elements (multiple players playing the same seed should have roughly the same game), but also when updating the game is means that if they tweak one area the rest of the seed will stay roughly the same. (Maybe less important for games with short runs compared to sandbox games like Minecraft where the world might be generated by very different versions if the game and you don't want blatent seams when it happens)