WHY AM I MYSELF RATHER THAN SOMEONE ELSE?

It is impossible for you to be someone other than yourself. Someone else is different (in some way) from you. If (somehow) you were changed to be the same as the other person, then you would no longer be yourself, you would be a copy of the other person. In short, if there exists anything at all attributable to you and only you, then you are you and not anyone else. Why is my reality being experienced from the perspective of my body instead of another? Why do I have this particular consciousness? For each individual reality exists within their own frame of reference. The result of this is that to each person experiencing the universe, the universe exists only within their mind. This makes you and only you. It would be impossible to be anyone else because there would be no one to perceive your reality.