One big reason is because they build better reputations, more and stronger relationships, and far bigger networks than matchers or takers. Reputation, relationships, and the right network will enhance anyone’s success in life.
Givers build more relationships and thus a bigger network because they’ve got a great reputation. Takers build fewer relationships and smaller networks because they sacrifice their reputation by acting selfish and not caring about the interests of others.
Givers succeed partly because most people are matchers who value reciprocity and fairness. The matchers grant a bonus to givers while punishing takers. When you’re a giver, the whole world is rooting for you and supporting you.