Overlap between Republicans and c/fuckcars might be minimal, but overlap between car enthusiasts and c/fuckcars is surprisingly large. It turns out that a bunch of folks who love the machines and the driving and the car culture are, in fact, capable of understanding that those experiences can get diminished when you force a bunch of normies to do it and clog up the roads.
Besides, in my case at least, the fact that I can use my bicycle to get around town means that all my cars can be project cars, instead of having to own something boring and reliable.