Founding a new Great American City

I looked up the top 25 American cities by population and then looked up when they were founded and came up with this list:

New York 1625
Boston 1630
El Paso 1659
Philadelphia 1682
Charlotte 1692

Detroit 1701
San Antonio 1718
Baltimore 1729
San Diego 1769
San Francisco 1776
San Jose 1777
Jacksonville 1791

Columbus 1812
Milwaukee 1818
Memphis 1819
Indianapolis 1821
Austin 1835
Chicago 1837
Houston 1837
Dallas 1841
Fort Worth 1849
Los Angeles 1850
Seattle 1851
Denver 1858
Phoenix 1881

I was looking for the date some kind of permanent settlement began, you could quibble over the exact year in some cases, but close enough for my purpose.

The last top 25 American city to be founded was Phoenix, over 125 years ago, by a guy who was just passing through and realized it would make a great place for farming if he built a little irrigation first.

Why did the founding of such cities come to an abrupt halt over a century ago?

Not a single one founded in the 20th century.

Anyone who has driven through rural American knows there are some great, virtually deserted places where a major city could have thrived if only America's pattern of immigration and expansion had been different or a major deposit of precious metals had been located nearby.

Nice climate, cheap land, pretty setting, lots of water, etc.

Just no jobs, I guess.

With so many virtual office workers who can live anywhere around these days, could they somehow get together and found a 21st century New York somewhere in rural America?