This is an interesting topic - I've read several books about this recently.
A full quarter of all US people have NO credit cards.
Another third do have credit cards but pay off the balance 100% in full every month (I'm in this group)
So only the remaining ones have *any* balance at all. So a group of them - with tons of cards - are the ones who make this "average" seem so high
That being said, I probably have 10, but most I never use. Store cards that have zero balance, no yearly fee, that I got at one point for a special deal.