Here are official statistics from the treasury department:
Government - Gift Contributions to Reduce Debt Held by the Public
While you are right, "it NEVER happens" is too broad a stroke, "many send money" is also too broad a stroke, IMHO. I mean, it was only $2.5 million last year. There are over 280 million Americans.
It is also tax deductible, like charitable contributions are. That's a bit ironic, I think.