I don't know the circumstances, but if I were you I would communicate with the current owner and ask why. The anser may be very simple, as a reputable breeder this horse is of breeding age, but is special needs, and therefore not breedable, perhaps the current owner just wants a loving forever home for a much loved horse. This is only an assumption and there may be other reasons, but it you open up and ask why, then I'm sure you will get an answer that is honest, as this person seems to me to have the best interest of this horse at heart. Many of us have given away horses to the person we feel will love him or her, and give them the care they deserve. If you need help PM me.
Terry