The 4-engine 747 saw passenger load shrink as competing 2-engine aircraft have become available. The Airbus A340 (1993) can fly longer trips. The Boeing 777 (1995) is more fuel efficient. The A380 (2007) carries more passenger.
More recently, even more efficient aircraft: the Boeing 787 (2011) and the Airbus A350 (2015) signified the beginning of the end for the 747,
* the first flight was by Pan Am, January 22, 1970