The number of passengers it seats is sort of a sweet spot, and even during bad times for the airlines, there are still plenty of routes that can maintain the nu

The number of passengers it seats is sort of a sweet spot, and even during bad times for the airlines, there are still plenty of routes that can maintain the numbers to make it viable to fly a 737. The 747 has a much more limited number of routes where it is viable, so there's less incentive for Boeing to spend money on it. But don't confuse the 737 of today with that of the original. There have been 3 major redesigns since the original (Classic, NG, and MAX), to the point where the MAX shares little more than the name with the original.