About 8.19m people have earned rewards of some kind on their plastic in the past year.
But only three million people have actually redeemed them, according to Sainsbury's Credit Card.
Four out of 10 people said the value of the rewards earned were too small to make it worth claiming them, 27% said the redemption process took too long and 24% said it was too difficult to redeem points they had built up.
One in four people said they did not know how to redeem their rewards, while 40% admitted they simply could not be bothered.
Donald MacLeod, head of cards at Sainsbury's, said: "Our research shows that the credit card industry has a lot of work to do if customers are really going to feel that their reward schemes are worth having."