Quad/Tri jets made great sense when twin engine planes were limited by ETOPS regulations. [1] A 3+ engine jet could fly routes that twin engine planes could not, which meant the 3+ engine lower fuel economy wasn't a big deal. When twin engine jets could fly across the large bodies of water on routes previously served by quad/tri jets, the superior fuel economy of twin engine planes became a competitive advantage. 747s, a340s, and similar planes simply couldn't compete in routes efficiently served by twin engine planes. The a380 is a great plane for an airline like Emirates which primarily serves Dubai because there is a lot of tourism demand for long haul travel on a jet w/ huge passenger capacity. If you can keep an a380 full, it's a great plane.

https://en.wikipedia.org/wiki/ETOPS