Suburbs exists because lawfulness reigns. Sure there’s ghettoes and dangerous neighborhoods, but by and large suburbs exist because, on the whole, it’s safe to move beyond easily paroled spaces. Cities, and before that, fortresses and the like, provided safety (physical safety at least, excluding disease) for those within their city limits. The smaller the space, the easier it was to manage safety.
In a place like the US, where lawfulness reigns generally, suburbs have been allowed to multiply. Lawfulness is fertile ground for suburbs to grow.