[dradtke]

I think the idea is to improve the sustainability of a city by reducing people's need to travel by car, which uses energy, and to improve its livability by ensuring easy access to most (or all) of life's amenities.

That doesn't mean it should be impossible to travel beyond the 15-minute limit. Other forms of long-form transit, like trains and cars, will always have a place, but not everyone thinks that they should be required to simply live.