By what definition are those 15 minute cities? You're retroactively applying a concept that has only recently begun being introduced.

In my experience, public transport in London is far from excellent. Compared to who? I've been here over 15 years.

Most Londoners living within zone 1-2 don't have a need for cars, what about the rest? Most people I know own cars. Every single house has a least one car in the driveway once you get outside of the center.

15 minute cities won't reduce traffic. They will reduce your ability to move around though.

The reason why we are against such things, is because once they are introduced somewhere, they precedent is set, and more restrictions will be brought in under the guise of protecting you and saving the environment.