Well, a related item is that airlines simply got tired of maintaining 4 engines (I'm putting it somewhat jokingly but not too far from the truth). For the not

Well, a related item is that airlines simply got tired of maintaining 4 engines (I'm putting it somewhat jokingly but not too far from the truth). For the not much better fuel efficiency and capacity, the complexity of the 747 4 engines are that much more of a headache to maintain properly.