The 747 has design roots that hark back to the days of the Boeing SST program, the 2707, although there is no engineering comonality, and the guy (Joe Sutter), who served as chief engineer on the 747 project was pitied for having been asigned this lumbering transport versus a spot on what turned out to be the stillborn SST.
The 737 has design roots from the same era, and the 5000th (albeit NG) 737 was delivered last December, with a huge order backlog remaining.
When your project is a subsonic transport, a lot of what matters was actually well known more than forty years ago, with many tweaks incorporated since.