Man I am so tired of the endless parade of articles with the premise "How could conservatives possibly think this?? Surely if we just take the time to carefully understand their reasoning we can blah blah blah...."

Here I'll answer the the "why" right now:
A) Most US conservatives live in suburbs and rural areas and generally hate and fear inner cities and the people who live there. They also generally hate and fear environmentalism. They also greatly resent the idea that the USA isn't the best country on earth at literally everything. They're also violently homophobic and have such deeply toxic ideas of masculinity that they consider it to be weak and "gay" to drive a smaller vehicle.

So when an urbanism advocate says they want people to give up their lifted truck to live in a city and ride a bicycle so the US can be more like Europe and East Asia to help the environment how in the world do you expect them to react in any other way?

B) This is a population that's addicted to hate, fear and opposition like a drug, and conservative politicians and news orgs are the dealers. They need to periodically find something new to tantrum about. If there is no reason to hate something then a reason will be created. This was the case with LED lightbulbs, with COVID, with Romneycare, and so on and on and on. The 15 minute city conspiracy theories are not some sort of new unprecedented pattern of behavior.