As much as I love horses in real life, I quickly came to dislike them in this game. A waste of 1000 gold coins. They die too easily. They launch kamikaze attacks against dragons and groups of bandits. I got excited when Bethesda brought out the horseback combat update, but that turned out to be awkward and clumsy to control. And if I am traveling to a new locale, I can just fast travel to the nearest spot and walk the rest of the journey, and I can hire a wagon ride to a city I haven't been to, so it's hardly a big deal.
At least with human followers, you can hand stuff over to them, they can follow you into dungeons, and they can't be killed by enemies. If they made horses unkillable (at least the named horses) that wouldn't be so bad.