I’m not sure it happens naturally at this point. It requires conscious action. I recently moved back to my suburban childhood city, and under the mayor’s directive over the last 10 years, they’ve been attempting to overhaul the town from a truly stereotypical American suburb of big box stores, chain restaurants, and completely unwalkable neighborhoods, to something denser and less car centric.
They’ve encouraged a lot of development to the “downtown” area, which used to be basically town hall and the library, to a place with a large central park/amphitheater with biweekly free concerts, a farmers market, and town festivals, lots of mixed use apartment/retail/business buildings, extensive bike/walking paths, etc. They’ve torn up an old train rail that was in disrepair that cut through the city and turned it into a pedestrian nature trail that connects the northern and southern parts of the city to the downtown core. They’ve partnered with private enterprise to develop a “test kitchen” that acts as a sort of incubator for chefs before they establish their new restaurant to encourage more varied and unique culinary experiences. They’ve developed an “IoT” lab to act as an incubator to attract tech startups to the area, as well as a makerspace/trade hub to connect employers and people seeking training in the trades. They’ve been working with developers to buy up old single family homes in the downtown area to develop into denser townhome and apartment complexes. They’ve done a lot of this over the complaints of the usual loud minority who screech about any and all change.
It isn’t all perfect, and there’s much to be done, and part of it was enabled due to the fact that it’s a relatively wealthy suburb, but it’s blown me away how they’ve taken what used to be the epitome of an American suburb and turned it into a city in track for something more sustainable. I could never have walked anywhere growing up, but since moving back, I’ve bought a bike and am strongly considering selling my second vehicle due to lack of use. But the point is that it’s all been active development by the mayor and the city council, at times over fierce objections by others.