Because the economy was pretty good in 1978, and the media didn't lie about everything back then.
11 million jobs were created during the Carter administration. Too bad that Iran decided to wait until Reagan's inauguration day to release the hostages. It's not too much of a conspiracy to think that there was some sort of deal there, similar to Nixon sabotaging the Vietnam peace talks right before the 1968 election. After all, there was the Iran-contra scandal later.