the zones are in 15 minute regiments and people are kept in these, by design, through removing their need to travel outside of them.
(Admission: I don't know what a 15-minute regiment is).
If you live in a major city you could probably live without travelling elsewhere. But people travel anyway.
the policy is designed to place all essential services for every human need within 15-minutes walking distance
Let's go back to the original example of a 15-minute city proposal on this thread, Oxford.
You might be aware that Oxford is a University city.
Are the colleges going to be disbanded, or are they going to be "distributed" so that each square mile gets a bit?
(Or each 1.099 square mile;
Let's say the average walking speed of a reasonably healthy adult is 5 km/h (roughly 3.11 mph) so in 15 minutes we cover 1250 metres. You could hypothetically
divide an urban area into squares, each side approx. 1.768km (about 1.099 miles), with services in the centre of the square- that way, the distance from the corners of the square to the centre is approx. 1250m, a 15-minute walk).
-Or the Mini (car) factory? How do you spread that about? Or the Bodleian library? Or the major trauma centre at the John Radcliffe hospital? The University and Mini factory are major revenue streams that "THEY" might want to preserve.
In reality, it's hard to see how Oxford City and Oxfordshire County Councils could guarantee that there would be specific services within each zone, outside of what local government is already obliged to provide- and often has problems providing.
County councils are responsible for education up to 16, social services, road maintenance, fire and rescue, and libraries (I think). Oxford City Council is essentially a district council, responsible for waste collection, some social housing ("council houses"), parking, planning decisions about proposed new buildings or conversions etc., and setting and collecting Council Tax.
A local council can't oblige a doctor's practice, a hairdressing salon or a grocery store to set up business in a given area, and wouldn't have the budget to hire or subsidise such services. Maybe a council could use planning decisions to prevent new services setting up "in the wrong area", in the hope that the service owner/ provider chooses to relocate to where the council wants- but they can't say "You WILL work THERE". I guess they could selectively reduce business rates as an incentive, not sure.
Plus, as I've pointed out earlier, in the UK, county councils and district councils don't control police forces. They don't have the power to physically coerce the population. Nor can they make decisions in conflict with primary legislation.
The police force responsible for Oxford (and Oxfordshire), Thames Valley Police, is operationally independent of local government.