It's not. Cities have literally been created from nothing in the last few decades. Just because NYC, Atlanta, DC, etc. are old are have a history of redlining does not mean that every city does. Case in point: the cities around where I grew up were built in the last 3 decades. Those cities didn't have a choice but to have zoning laws and miles of road.
I live in Seattle, for instance, which used to have a network of rails. They've all been torn out and we're just now putting them back.
1. get rid of zoning laws that prevent building multi-family units.
2. invest heavily in public transit. Buses are great if they are widespread and arrive frequently.
3. in areas that have significant traffic, use trams/subways instead of buses. They carry way more people and don't sit in traffic.
4. make city centers dramatically more walkable. A 4 lane street is much harder to cross than a 2 lane street (or 2 one way 2 lane streets).
5. don't build new roads/highway exits that will encourage further sprawl.