"...how in the world could the AVERAGE be 10,000?"
It's our instant gratification society. Kids, when they begin working real jobs just assume they should be equal with mom and dad. Back in the day, we bought used cars and starter homes. Now they build the big new 2500 sq. ft. home and buy two new cars. That is how many get into it. It's a trap. They feel pressure to take on enough debt to get all those things now.
And then there are those that just have a run of bad luck, unexpected illness, etc. $10k in expenses can happen pretty fast.
Given those two groups, I can see the average cc debt being $10k.
Don't forget that there are considerable quantitites of debt which were incurred responsibly, but which is reported in the same way as consumer debt.
For example, I was able to refinance a significant slug of my law school loans at 3.99% with no expiration date on the rate -- far better than even my prior official refinance rate, particularly given that I lost the student loan interest deduction due to phase out. While these low-single-digit, no-expiration-date transfers are limited to those with good credit, they're very attractive when you can get them. I know plenty of people who've done those trades with higher interest student loans, car loans, and other big debts. (In addition to cheaper interest, the trade also gives you a far better downside protection: the credit card issuer can't repossess the car, and doesn't have the benefit of non-dischargability in bankruptcy that the student loan lender had.)
Nevertheless, credit card issuers report those large slugs of cheap, long-term debt the same way as it reports people who've been borrowing at 18% to buy groceries for two years straight, even though the debts are (economically) unrelated.