Why is my rear drivers wheel tilt in on top

That is called negative camber. Negative camber is when the top of the tire tucks inwards. For a road going car you typically want to maintain a slight amount of negative camber (1 – 2 Degrees) to improve road handling. Camber improves handling by allowing the tire to apply even loading when the body rolls going into a corner. A good Alignment shop can put in a kit to fix it or you could take a whack at it yourself. Cost a lot more than a regular alignment though.