The Tri-jets (L1011, DC10 etc) were a compromise as at the time legislation did not allow twin engined a/c to fly transatlantic.
Better engine/system reliability and maintenance/operational experience created the ETOPS system.
The rest is history.
Podded, wing mounted engines are a lot easier to maintain and replace. They also tend to be closer to the ground so inspection access is easier and requires less ground support equipment (steps).