(Of course, this assumes you never carry a balance on your card... and why would you?)
I'd guess it's because you don't have enough money to get what you need, so you charge it.
Nope -- that's NOT why most people carry a balance on a credit card. They "don't have enough money to get what [they] WANT."
Yes, there are lots of poor people out there in dire straits, but most of them can't even qualify for credit cards, because they don't have reliable income or whatever credit history they have is bad. The people who charge extra on credit cards are typically people who have enough money for what they NEED, but they WANT more stuff faster than they can make money to get it. If they really NEEDED something, there are often ways to take out loans that would give a better interest rate than a credit card, or they could get government assistance or something if it's a basic human need.
The other group of people who carry a balance are the people who usually did pay off their balance in the past, but they've lost a job or had some other unforeseen expense. Most of these people could also have been saving more for a "rainy day," but I have a little more sympathy for them. And there are some for whom the "rainy day" has lasted so long that it depleted a reasonable savings... they should perhaps not be faulted either.
But most people just use credit cards for crap they don't need that they can't afford, but they want it NOW. And I personally think that's a stupid financial decision, because at credit card interest rates, it will cost you more in the long-term than just waiting a little while to save up or just buy something more affordable that will work in the meantime, like responsible adults do.