The pretty much universal abuse and welfare issues surrounding horse ownership is why I gravitated away from horses and toward dogs (professionally) in my youth.
Pretty much all of owning a horse means compromise and it is the horse that does the compromising, not the human.
Horses are meant to be wandering around over many miles per day, eating as they go, dozing periodically, covering a variety of terrain and existing on a continuous trickle feed of low calorie grasses.
They live in social groups from just a pair that may shift and change over time to large groups.
They are adapted for dry climates, but varying temperatures.
What do we do to horses?
We keep them in isolation, we stop them moving, we stop them forming social groups or force them into groups they would not choose that cause them stress. We prevent them grazing because we keep them on wet ground with high moisture, high calorie grass (designed for grazing cattle on to produce milk/beef), then we feed them grains to provide the calories they failed to get...
We shut them into tiny spaces, ride them long before their bodies are done growing, breed them to have non-functional conformation and a predisposition toward painful conditions (look at the stats for how many Thoroughbreds have kissing spine), train them using positive punishment and negative reinforcement almost exclusively.
We hack up their feet because we stopped them moving naturally and freely over terrain, we fuck up their mouths with bits or their faces with pressure halters, their backs with saddles, their ribs with girths.
And then bitch and moan that our horse is an 'asshole' and 'naughty'.
This of course, isn't everyone - but it is the majority unfortunately because most people don't own land, or sufficient land to keep horses appropriately anyway. With the best will in the world, it is impossible for most people to meet all of a horses demands, and so much of it is accepted as 'the norm'.. because it is so common.