It's weird to me ...................why do excellent people gather in the same place?

It's weird to me that excellent people hang out in certain areas together.... my question :  how the hell does that happen or start ??

Topical Example :

Music - Seattle  :  From the 90's w/ the whole grunge movement to today's hip hop resurrection w/ Blue Scholars, Dyme Def, Common Market

Technology - Silicon Valley.....  please do I have to mention the companies?

Cultural Example :

Armenian's :  Sherman Oaks

Vietnamese : Fountain Valley

Religous Example : 

Mormon : Utah

Amish :  Pennsylvana

Business Example : 

Woodworkers : Slater Avenue, Huntington Beach

Bodyshops : Slater & Newhope, Fountain Valley, CA

Shipping Companies : Memphis, TN 

Is it weird or am I just tripping ?