Shortly after Ronald Reagan won the presidential election in 1980 he leaked to columnist Jack Anderson his plan to attack Iran after he took office in January 1981. Anderson reported that Reagan said the American hostages being held in Tehran were expendable. The U.S. would target Iranian military and industrial targets with conventional missiles launched from ships. The Iranians released the hostages the day Reagan was sworn into office
Also I recall reading that Khomeini hated Carter and wanted to embarass him by waiting until he was out of office to return the hostages