Here's how I interpret their reactions:
Conservatives tend to have much larger amygdalas, which makes sense, as their worldview is based around fear. The brain/ amygdala treats threats to personal identity with the same fear response as physical threats.
A 15-minute city means you don't need a car, and it's far less convenient to have one. But for a lot of people, especially the conservative folks, their car (or bro-dozer) is their identity, or at least a huge part of it. Their identity is fragile enough already, it can't withstand removing a big chunk of it. (How would a man know he's a man without a truck to perform masculinity in?)
Therefore, a walkable city is s threat to their vehicle, which is a threat to their identity, which is just as frightening as a physical threat, like being hunted for sport.