I know what I'm about to say may go against popular opinion, but hear me out:
The only two reasons I can think of that may explain why horses die so easily even down a small slope, and why SV has decided to make them that way in MO2:
First, I don't know how many of us have ridden horses across the untamed countryside. Apparently, horses have very delicate legs and the way their body is structured makes it easy for them to be seriously injured.
But I think many of us may have been conditioned by Hollywood to think that horses are invincible warhorses that can go anywhere without getting seriously injured. I was reading these articles and was surprised to find out how fragile horses actually are in real life:
Backcountry riding has a lot to offer, but only if you’re prepared for its possible dangers. Here are eight backcountry bugaboos to watch for and ways to safely navigate them.
horseandrider.com
While this question could come as a surprise for the non-initiated, anyone who has spent time on or around horses will know horses are forever getting injured, lame and sadly often worse. Horses are mostly big animals, seen as powerful and fast. Why is it, then, that they are so fragile? The...
www.naturalhorsemanshipindia.com
Horses are fragile because of the small bones in their legs and their sensitive digestive system.
horseracingsense.com
Second, I think SV may have made horses this way for balancing reasons. On the flat plains, mounted fighters and archers absolutely dominate, and those travelling on foot stand little to no chance of going toe to toe against them. For those travelling on foot, sloped terrain is probably their only defence and best friend against them.
I think SV intended horses to negotiate sloped terrain while the rider is dismounted. Again, this may be for balancing reasons and I have found myself having to dismount often in my trips across the countryside.
I have found that they do far better going down sloped terrain while I'm dismounted, and on many occasions I have seen other players doing the same thing. They take virtually no damage, and the creature pathing system will take care of the rest.