Metal is damned expensive, and if you think every horse that decides to serve just ups and gets free metal armor you're insane. That would bankrupt the kingdom!

Some have to make do with shoddy leather armor- well not shoddy; just not metal. This was me working with the concept- the leather over the nose and forehead were going to be much harder leather, kind of like a shell, where as everything else was going to have some metal studs, a strong reliance on the the virtues standard leather.

They're terribly uncomfortable and well hated. Though, many swear by them; in a pinch that is.

Also, hoof.