Yep they just didn't do the maths
2 engines are more economic than 4 in the size planes that airports can take
A huge amazing shift in technology... Who'd have thought that twins would be flying ~20 hour legs between cities instead of flying to hubs and offloading onto 747s or 380s...? 
Watched a great video the other day about 777 and A350 developments, amazing stuff!
777 has been an amazing plane, I don't know much about the A350. In the early 80s I spent time at Boeing Seattle (on military interfaces) but all the time they were test flying the 757 and 767 and it was great to watch. The 757 was a bit of a dud but imho that 767 was the 2 engine game changer that led to the 777
Any list please to the video