Oh yeah; horses are a huge adoption-needing niche. People basically show them until they are not earning anymore money, get hurt, or are not breedable.. and then ditch them at a rescue. Others end up being there after suffering neglect; their feet get bad and no one wants to buy them, so there they go.
It is really sad. i can only afford time-wise the ones we have now; I would love to be a millionaire and buy huge amounts of land and just rescue/care for a thousand horses.