What Killed the Trijets?

Once upon a time, airports of the world roared to the sound of three-engined commercial airliners, ranging from smaller regional craft like the Boeing 727 and Hawker Siddeley Trident, to flagship long-distance wide-bodies like the Douglas DC-10 and Lockheed Tristar. Today, though, they're all gone, their demise steeped in the inevitable rise of twinjets as focus shifted towards fuel efficiency and environmental considerations, something the trijets weren't equipped to handle.