Cars are really just another toy for the rich they're all handmade and personalized. Just ridiculously expensive for the common man to afford. All you need to make horses is a boy horse and a girl horse. Horse shows, horse markets, and horse races are also huge social events and activities ingrained in most societies across the world. Now the less expensive motorcycle has a chance of replacing the horse I think it's become increasingly more popular especially among the middle classes and diyers who like to modify bicycle frames. The only thing I can think to change this is if that madman Henry Ford had succeeded in his plans to change the way items are produced but he was debunked as racist control freak long ago, hard to see anything he came up being adopted on a large scale people just didn't like him. Also there's no standards for automobiles there are steam cars, electric cars, hydrogen cars, and petroleum powered cars what if you run out of fuel in a town that doesn't have the type you need, better infrastructure needed, likely you'll just wish you took the train instead.