The Boeing 747 is not for every major air carrier. At one time, TWA and American operated 747s, but they were phased out when it became clear that two-engine transports could be safely operated on long routes where there few or no nearby landing fields which could be used if necessary.

Compared to such aircraft as the Boeing 767 or the A330, the Boeing 747 is often regarded as being too expensive to operate, especially on routes where not too many passengers will be flying. (Until the safety of the two-engine design was demonstrated, American, TWA and Delta would often use three-engine transports such as the L-1011 or the DC-10 or even smaller four-engine transports such as the Boeing 707 until they were retired.)

I understand that Delta briefly operated four Boeing 747s during the early Super70s, but they were regarded as being too big for the airline's routes.

--Anonymous