I’m not a ‘horsey person’ at all, but I have a daughter who is, so I’ve had to learn.
Horses are not pets. For starters, they’re huge and could quite easily kill you.
They have their own minds, personalities, likes and dislikes. Some don’t like jumping. Some don’t like beaches, water. Some need to jump, or live for eventing. You absolutely can tell when a horse enjoys something and when it doesn’t. I can, and honestly my horsey knowledge could be written on a postage stamp.
If you have a horse that lives to compete (genuinely seen them, know them) and a person who does not want to compete and just want to plod around a field, that horse will be both bored of out of its brains and miserable. That’s also a dangerous combination. And person, horse or both could end up seriously injured or killed. Likewise, if you have someone who is competitive and a horse who just doesn’t have the heart for it, but would love to wander round, out for hacks in the woods etc - they’re not a good match either. If they kept it, but also got another, it would be neglected emotionally at best.
Horses connect with their riders. It’s a partnership, a relationship. Relationships have to work for both parties, or you move on and find a better fit.
There is also the financial burden. At one point, my daughter had 3 ponies - one she was riding, one she was riding but really had outgrown and one she was going to essentially grow into. That cost me £20,000 a year for their livery. It was fine at the time as all were needed.
A year later, one needed to retire (he was loaned so he went back to his owners and lived out his days very happily in a field), and the other was completely outgrown. But she was young and she absolutely loved being fussed over by little ones - it made her so happy. She was therefore sold to a lovely family who had 2 little girls who wouldn’t outgrow her for 10 years (the youngest was a baby). If we had kept her, it wouldn’t have been in her best interests. She was young, bright and wanted to ‘do a job’. She would have been completely miserable. We keep in touch and she’s so happy, the little girls are so happy and we see them at Pony Club and she is clearly well loved and looked after. Keeping her, finances aside, wouldn’t have been right for her.
So now we are down to one pony.
What I would never do is sell or pass on a retired pony (or one close to retirement). They deserve to live out their days happy, with other horses and humans who they know.