The point is that it makes some bits nicer for rich people, while the poorer people are forced out of these nicer areas. As someone further up in the comments said, they pay a premium for this, while many people are having to use food banks just to feed their kids etc - they can't afford to pay a premium to live somewhere they can walk places.

And anyway you can't have the entire place be 15 minutes because some people have jobs etc that are just incompatible with that, and they tend to be lower income people.

It's essentially "economic cleansing" so only the nice charming rich people with interesting jobs doing something awfully smart in tech can live in the lovely areas with the nice cafes and that lovely little grocery store that does that tapenade to die for. Meanwhile the lower income folks live further out in lower density cheaper areas that need cars and have the run down high streets with the vape shops, the betting shops, the drug addicts living in derelict doorways etc.