Because you are you and if the whole world were the same, you could never be told apart from everyone else, only you would know who you are, but then you might get lost and never find you way back to whats inside you heart!
One Taste is not some experience you bring about through effort; rather, it is the actual condition of all experience before you do anything to it. This uncontrived state is prior to effort, prior to grasping, prior to avoiding. It is the real world before you do anything to it, including the effort to "see it nondually".
This is the world of One Taste, with no inside and no outside, no subject and no object, no in here versus out there, without means, without path and without goal. And this, as Ramana said, is the final truth.