Okay, maybe it's just me and I've never seen it, but I've been doing a lot of ground work with my yearling (Shotgun) the past few weeks, including trailer loading.
He has already been on trailer rides to the farrier and vet in my parents' huge stock trailer, and he hops right on that and travels fine.
But the horse trailer I was borrowing for the time being was a slant load with rear tack (and just like the one I bought today!). So that's difference to load in than a wide open stock trailer.
I was so proud of him. First time I asked him to load, he followed me right up, no questions asked, and back off super! Twice! I was so happy with him I called that a sesson. The next time, I close the butt bar and the windows. No problem. He's doing great. Next step will be to go for a ride. But, I am just amazed at how naturally slow and calm and SOFT he backs himself off the trailer; especially his front legs.
He locks the opposite leg, so that he can lower the other leg to the ground, and unlocks it at just the right time to quietly step down. I had to take a video of it yesterday, I am just so amazed by him.
Maybe lots of other people's horses do this, but so far, none of mine have been real "graceful" backing off!
Excuse the dumb iPhone format.
Edited to add that yesterday I was just working on front feet on and off into the back stall so he learns not to just leap onto the trailer.