Televangelists - why do people donate money to them?

I saw this program on TV about televangelists. One in particular who lives in a 18000 square foot mansion by the sea, has several private air planes, vacation homes, cattle ranches and more. Millions of dollars flow into his mission from all over the world. A lot of the donations come from people who can ill afford to give it. He promises prayers and that their donations will lead to personal wealth and well being. I don't understand this at all. Any ideas why people give to these ministers?