1. Volume. They've sold so many 737s they're scared to upset the market. 747s 2. Target market. There are airlines like Southwest and Ryanair who use a lot of

1. Volume. They've sold so many 737s they're scared to upset the market. 747s 2. Target market. There are airlines like Southwest and Ryanair who use a lot of 737s and have optimised their routines around very specific aircraft, so want as little change as possible. In comparison the bigger aircraft are used more by the legacy carriers and flag carriers, who are more used to operating a mixed fleet and more willing to try something new.