I realized part of the problem recently; if you can afford to live in a 15 minute bike city, you're also living in a 5 minute car city. (Or more precisely, if something is a 10 minute walk away, it's about a minute or two by car.)

Until you go from one car to zero, the car is a damn good temptation.

I just did a round trip to pick up something from the library, a mile away. Could have walked, but couldn't have walked and got back in time before my meeting.