Faster horses would have been terrifying and dangerous. Have you ever ridden a fast horse at full gallop? It takes quite a bit of skill just to stay on and maintain control; you generally can't just let the horse "drive" itself.

The point stands, however. John Wesley, founder of the Methodist church, would read and write sermons as he rode (obviously not at a full gallop) from church to church, if legend is to be believed. These days he might, at best, listen to a few podcasts as he sits in traffic.

If he had a car he would have arrived at the church fast enough to have time to read and write after he got there, even with traffic. Especially if you factor in the extra time it takes to care for a horse and deal with the tackle.