If 25 people have 4 credit cards each and 75 people have none, then we have 1 card/capita, but only 25% of the population uses credit cards.

The median seems to be 0.25 cards/capita. Your own source already ~agrees that they're "not a thing for most people" (if we're really pedantic we can start looking at populations of those countries), but to find a more realistic estimate for the percentage of the population who use credit cards we would have to divide this figure by the average number of credit cards among people who have at least one.