I imagine if they're not known, they will be in time.
Sometimes people just get in a bind though and would rather they go to a good home.
In spite of the many shady characters around (including in the horse world, lol) I can personally verify how true this is!
In my many years, I've been given horses for free, and also once gave away a horse for free. All great horses, none of them neglected, unsound, untrained, or any issues, just due to life situations of the owners.
The first one given to me:
Good friends who were the breeders of my event horse had a devastating terminal health crisis and needed to find new homes for their horses. My horse's sire was a Trakehner stallion, 4th-level Dressage trained, but by this time he was over 20, not breeding any more and a bit arthritic. They LOVED him and were happy to give him to me if I promised him a forever home where he would be ridden lightly, graze a lot and have other horse friends nearby, and a humane ending when that time came. They also had the stallion's 2-yr-old son (my horse's full brother) so I took the old stallion for free with my promise to take good care of him for life, and I bought his colt son for a good price with my promise to start him when he was older and sell him to a great home.
I had the old stallion for 6 more years - he was such a sweet boy, showed off in front of the mares by prancing with arched neck and snorting, but was never rude or pushy or hard to handle. He was a joy to ride 2-3 times per week, he taught me so much about what an advanced horse should feel like.
At 26, he started losing weight and kept getting thinner, even though he ate all his food including increasing amounts of soaked beet pulp and alfalfa pellets. The vets tried different things, took blood, tried steroids, finally a biopsy showed he was suffering from liver cancer, and when he got too weak we said goodbye.
A few years later I was going through a really nasty divorce, had to quickly get the heck out of a bad situation and leave my farm for an apartment. I had 4 horses at the time but could only afford board for two. The two I kept were the old stallion and my event horse. The youngster by this time was solid at WTC and good on trails but still green - I care-leased him with option to buy to a talented teen, who bought him a few months later and achieved great results with him in the local Dressage scene.
The 4th horse, who I gave away, was my Appy mare, bought at at 17 or 18 for cheap, to be nothing more than an older companion for my first youngster. She was good for trail riding at first, then proved herself to be sound and energetic and willing to try new things, so we tried low-level Eventing and various classes at local shows just for fun until my baby was ready. She won two 1st places in her first Cross-country derby, individual and pairs, good results in many low-level Events and local shows, hilarious prizes due to her knowing what she was doing though I was clueless, saved my life on a trail ride one time... So many stories I could tell about her deserve her own thread, if not a book! She was such an awesome mare, I miss her.
Once my youngster was older and I was riding him, I leased out this mare to an awesome pony club young lady who did great with her and learned a lot, but after a couple years was more advanced in her riding and ready for a new horse who could take her to higher levels.
Unfortunately, my mare's lease ended at the time my abusive divorce situation meant I had to find new homes for two horses. I'd promised to keep the old stallion, his older son was my heart horse, his younger son was on a care-lease-to-own which was turning out great, so unfortunately I had to find a new home for this awesome Appy mare who was now 20, and a friend of mine had a good situation. Her niece had recently lost her elderly horse, they owned a nice property with other horses, the young girl was more into low-impact disciplines like trails and halter shows suitable for an older horse, and they were experienced horse owners. So I gave my mare to this family. I hauled her across the state myself so I could see how they would be keeping her, they had a nice pasture with other well-cared-for horses, the little girl seemed thrilled to hug her new horse, the adults seemed happy and knowledgeable, so I gave my wonderful mare to them. And they sent me updates and pictures.
I still miss this mare, and wish I could have kept her. Though she'd be 47 by now, so RIP my sweetheart.
The second one given to me: I actually paid 1 dollar for her just to make it legal, so she wasn't actually free.
A friend of mine who is a trainer used to go to auctions or buy horses out of the kill pens to find horses who might need some medical procedures or training which might have been neglected, in order to be good horses for her lesson program. The local auctions these days never have cheap horses, but back in 2010 my friend bought Fiona out of the killers' pen. Fiona was a cribber, in skinny condition, sweet and easy to handle on the ground except unwilling to trailer load, anxious under saddle, threw her head around in all directions at the slightest touch on her mouth. Needless to say, Fiona wasn't a good fit for my friend's lesson program.
My horse was on stall-rest and hand-walking due to a recent hock surgery, and needing someone to ride, I approached my friend to see if she would let me try out Fiona. And we got along great! She was super forward, loved to jump so much that she would leap over a pile of manure in the arena as if it was a meter oxer. She freaked at any touch on her mouth, but was super responsive to seat cues, you could slow her with your weight easily and turn her by stepping down on the inside stirrup. I loved riding her and my friend was happy to half-lease her to me.
When I left that barn my friend had rescued other horses that were more suitable for her lesson program, so I was more than happy to buy sweet Princess Fiona for $!.