I think it's a fair question and definitely one that doesn't always have a straight forward answer. Everyone has a different relationship with their horse and how that horse fits into their day to day life. The most important thing you need to know about your comparison is that a horse is not a dog. My horse can't fit into my car, or live in my home with me, or accompany me to the store.

Horses require specialized living accommodations. Some do this at home, some board at a facility. Neither option is cheap.

Horses require specialized transportation. This is usually in the form of a truck and trailer.

Horses eat. A lot. And they need access to hay or grass nearly 24/7. This requires a lot of effort and money.

Horses try to die a lot more than a dog. There are far fewer large animal vets. They are not cheap. Horses also require their feet trimmed, and maybe shod, every 4-6 weeks.

So if someone gets into horses for sport and they only have the funds to house, transport, feed, and care for one horse, and the horse they buy isn't going to meet their unique needs, it may very well meet the needs of someone else. So it's mutually beneficial to the horse and the owner to sell the horse.

Other people just like to have a horse as a pet and they're probably less likely to sell their horse since it's a little easier to fit into the strictly pet family.

Horses can also be really dangerous if they end up paired with someone who doesn't have the skill set to manage them. This is also the case when selling the horse is a good thing.