Because it's like a loophole that allows racial segregation without implicit, legal segregation. It also keeps poor people restricted to certain areas due to lack of public transportation or meaningful ways to get around except for cars. It generally keeps everyone away unless they have a reason to be there, since the sprawl type of suburbs are endless repeated houses full of paranoid white people who are possibly armed.

Chuds like when white people are kept in little sealed bubbles apart from the world, yet destroying it with their unsustainable sprawl lifestyles with grass lawns in Arizona.

Also suburbs like that are like little battlegrounds where people like to pretend they're little capitalists who've made property investments. So their home, rather than being a practical place where they live, is more of a long term business strategy to make money later. So your neighbors are both competitors and allies in this scheme. If they don't keep up appearances, your property values drop, so you get to be a little annoying hall monitor by calling an HOA and complaining your neighbors grass is too tall.