Ok. I'm no expert here.
But the A380 wasn't competing with the 737. It was competing with the 777, mostly. And a 777 can give you almost 400 pax on 2 engines. There have been 2,000 orders for 777s.
The reason that's relevant, btw, is lower maintenance cost per per passenger mile.
(That's why almost no one bought new 747s either, and that line is being retired as well....)
Right, That makes sense. The industry is definitely trending toward the more efficient 2-engine aircraft on long-haul routes. I just don't think "passengers per engine" is metric anyone would use. Cost per passenger is dead on.
But the A380 was aiming to cater to what Airbus felt was a previously untapped market. In a normal 2 or 3 class config., the 777 is still carrying about 150-200 fewer passengers than an A380. And the 777 was around long before the A380 was. So again, it was a misfire in identifying the market direction. At least with the 747 which has been around nearly 50 largely successful years, you can make the case for obsolescence (and the 747-8F is still very successful). The 777 came about as a challenger to the tri-engine widebodies (DC-10 and L1011) because Boeing realized that the future of long haul travel will require a more efficient aircraft. Airbus had the success of the 777 to look at (the 777 launched in the mid-90s) and still thought the whale had the potential to be a big success. It was a mistake.