While we have a variety of purposes and needs for our horses, we also keep them alive by breeding and protecting them extensively. The reason for this is that horses themselves are very fragile creatures and have a hard time surviving in nature.
If it were not for the fact that humans used them for walking or fighting, and carefully cared for and fed them, they would have died out long ago.
Horses have many shortcomings, such as being too thin and fragile in the structure of their limbs, and being too obsessed with speed at the expense of other aspects. Once one limb is injured, the weight on the body puts a greater burden on the other limbs, leading to rapid deterioration of the condition. A broken leg means certain death.
Although it eats grass, it is suppressed by even-toed ungulates because it has no ability to chew food. Horses have also struggled in recent years, like Africa's most powerful rhinoceros, which is now endangered. The North American horses were even worse off, disappearing before they were domesticated by the natives.
Perhaps some people will wonder, at the speed of horses, without any natural enemies, without any survival pressure, grassland everywhere is green grass, why they are endangered?
In fact, although herbivorous horses have a lot of grass, their energy conversion efficiency is not high, most of the time is foraging, and they do not chew grass, so their eating speed is much slower. If the weather changes too much, or if the winter is too cold, then they will starve or freeze to death.