Originally Posted by J. Falcon

I think this one is easy to tackle.

Remember in the original 1955/1985 Biff hadn't tried to rape George's wife. They met when George fell out of the tree and that was that.

In the altered 1985, I guess Biff simply turned into a sorry loser (kind of like George had been) and over the years George gave him degrading "pity" jobs like waxing the car, etc because he felt sorry for him.