The numbers are very skewed. There are a few people at the tippy top of the mountain, the Mark Zuckerburgs, the Bill Gates of the tech world, and the hedge fund managers of Wall Street, the film and media industry in LA. These people and industries drive up the GDP of an area. Also, SF and San Jose do not have large really bad inner city areas, the way LA and Philiadelphia do. What brings down cities like LA, Philadelphia and NYC are the large populations of people not doing so well. So the average is meaningless. What happens if you don't include the top 5% of earners, then what do these cities look like? And how much of the GDP is the high cost of living in so many of the high finance and West Coast cities.
I'll lay odds Des Moines, IA is a pretty nice place to live, and not as expensive.
So the message is: Work in a city, make a ton of money, then get out and go to a lower COL area in retirement.