Relying on individual's changes will lead to what we've been doing for 30 years. It leads to the current situation of “penny wise and pound foolish”, saving water when brushing teeth but taking planes.
This. I pissed off my ex's sister once when she said that since she was moving 40 kilometers outside of the city, she and her husband needs two cars. I asked her why she was moving then, you already have a house with a room for all your kids close enough to work that you can bike. She answered that she loves nature, and just going for a run there whenever she wants. So I said "wouldn't you then say that to go for a run in the woods whenever you want, you'll get two cars"?
It sort of killed the mood. I'm a monster.
In most cities it's simply unaffordable to live in biking/walking distance to the city centre. And the jobs are there.
Also, there are trains, subways, etc, that has a very small environmental footprint. Bicycles can also take you a fair distance, especially the electric ones.
If there is a will, there is a way.
This goes for a lot of cities in Sweden, it comes down a lot to culture. In Copenhagen 40% of the inhabitants bike to work, in Stockholm less than 10%.