Because those policies are never just let us build what we want; it is always only build what we want. Every single city where urbanists have taken control has enacted policies like mandatory parking maximums, raising taxes on cars and gas, banning the construction of new suburbs with urban growth boundaries (the main reason besides immigration for the rise of housing prices), removal of infrastructure in order to make driving slow, etc.
If urbanists just wanted to a car free neighborhood no one would care. In fact, they could do that right now by buying some unincorporated land near a city and building whatever they want on it. They don’t, because the actual goal is to force everyone into their preferred lifestyle.