About cities here in the USA?

Starting at 2018, there are 19,495 consolidated urban communities, towns and towns in the United States. 14,768 of these have populaces under 5,000. Just ten have populaces over 1 million and none are over 10 million

That's just the way it works, usually because of infrastructure like water plants, power stations and airports.

Kansas City takes up large portions of three counties.

Some cities like Baltimore and St. Louis aren't in any county.

Louisiana and Alaska don't have counties and Hawaii only has counties, no cities. 

Because the county borders were drawn in the 19th century, when Dallas was just a small settlement.  In the 20th century the city grew and spread out over the county lines.

If you think Dallas is complicated you should try New York City which occupies the territory of five (!) entire counties and its suburbs spread over parts of three different states.

Some towns are in 2 different STATES. Two examples?are Texhoma and Texarkana. Much of Hooker Oklahoma?works in Liberal Kansas, or they used to but Wal-Mart closed the Liberal Wal-Mart supercenter. 

Greater Oklahoma City includes at least 5 counties and up to parts of 10 counties including Edmond, Norman, Noble, Blanchard, washington, Jones and other towns. 

Cities started small, and some grew massively covering multiple counties, and sometimes even states.

Communities came first, counties came second.