Fundamentally, consumers and producers are at odds with each other in certain ways. For instance, it's best for customers if every shop was open 24x7, but absolutely horrible for the employees needed to make that happen.
Walmart is the extreme end of satisfying consumers above all else. Customers get a single, climate-controlled location to take care of nearly all their shopping, with good prices; but it comes at the expense of the employees, local community, and factory workers. Unfortunately, most customers don't know or care about those downsides because the experience is catered so heavily for them, and it's hard to get people to sacrifice material comfort for benefits that appear so abstract.
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.
Walmart is the extreme end of satisfying consumers above all else. Customers get a single, climate-controlled location to take care of nearly all their shopping, with good prices; but it comes at the expense of the employees, local community, and factory workers. Unfortunately, most customers don't know or care about those downsides because the experience is catered so heavily for them, and it's hard to get people to sacrifice material comfort for benefits that appear so abstract.