What I heard was that, at the time Jeopardy first came around, there were other trivia quiz shows that had been involved in scams by giving answers to certain contestants they wanted to win (because those contestants were more popular and would increase show ratings if they continued to reappear on the show). Jeopardy thought they were eliminating the potential for that kind of cheating by giving everyone the answers, and the contestants would have to figure out the questions instead. Obviously that doesn't solve anything in practice, but I guess it caught on.