It's a strange one.
When the 737 was built, the aircraft industry thought that the supersonic transport (SST) was going to be the big thing. In particular, being so much faster, it could get more flights in per day and have a much lower cost per seat mile.
That didn't happen, and the 747 turned out to be the future instead. Through the 1970s and 1980s there was intense competition for widebody planes, but the 737 slowly gained in capability and gained market share.
The 777 was developed just as the Boeing-Airbus duopoly was settling into place; in some ways it is an answer to the A300 (make a huge 2-engine airliner and make it so reliable you can fly over sea), but a greatly improved answer. 777 found product-market fit, but Airbus blazed the way with the A330/340 which you could get with 2 or 4 engines respectively.
The 787 not so much. When it was originally conceived, fuel prices were low and Boeing wanted to make a "sonic cruiser" that traveled at just below the speed of sound but a little faster than current jets.
(Here is the business jet version of that)
https://en.wikipedia.org/wiki/Gulfstream_G650
Then fuel prices spiked and they made a plane for balls-to-the-walls fuel efficiency, then fuel prices dropped. So it wasn't really the airplane that airlines wanted.
The A380 is the canonical advantage of a good plane at the wrong time. It came in as a 747 competitor just as the 777 and 787 started to eat the 747's lunch.
Given that the lifespan of a plane can be so long I can't blame plane makers for being apprehensive that they're going to invest a lot of money in a clean sheet design that the market may or not be interested in by the time it is ready.
The A320 is similar to the 737 in terms of materials, but it has a fly-by-wire system that Airbus has perfected and proven -- it's flight-envelope protection capabilities is as far ahead of MCAS as Chess is to Checkers.
Airbus has made the A321XLR which is a scaled-up A320 to a much larger airplane than Boeing can deliver with the MAX-ed out 737 platform.