Why is each character in "The Rocking-Horse Winner" motivated to acquire money?

The two characters whose motivations we gain insights into are the mother and Paul. The father remains in the shadows, seen through the eyes of the mother, while the uncle and groom simply seem to have a reasonable, healthy enjoyment of betting on the races. The mother, however, has an empty spot in her soul that she tries to fill with money; however, as is almost always the case with inner emptiness, money simply can't fill the void. She is dissatisfied with her husband and, we are told, is incapable of really loving her children. Money becomes her substitute for love, and the house is permeated by the sense that there is never enough, despite the family's comfortable lifestyle.

Paul goes on his endless quest of riding his rocking horse to win money for his mother because he senses her emptiness and wants to make her happy and earn her love and approval. He gives all his winnings to her. He eventually rides himself to death to win money, money that he doesn't want for himself, in the attempt to fill his mother's void.