In less extreme times, the US Forest Service routinely blows up carcasses of fallen horses – after removing horseshoes to minimize the hazard from flying metal debris – to prevent gatherings of ravenous grizzly bears that frequent Wyoming’s open spaces.
It probably doesn't make economic sense if the carcasses are in hard-to-access locations, but it is a little unfortunate that the hides can't be used.
Back in World War II, bomber jackets were made out of horsehide leather, because it was very tough and durable, and because there were lots of horses in use, so there was a ready supply.
But today, there are far fewer horses around. They've mostly been replaced by motor vehicles for transportation or farm work, so horsehide is in scarce supply. As a result, if you want an actual horsehide bomber jacket, it's pricey. It's more common today to use cowhide for leather stuff.
Makes them break down easier/faster and less logistically challenging and costly than taking them somewhere to be composted. Also stops grizzly and whatnot from gathering at the horse.