Some horses will - some won't - ever.
Our horses come when called. The only time they consistently get a treat is in their feeder right before lights out.
A horse will come if they enjoy what they are doing. If they are in fear or pain, they won't come.
I strongly disagree with this ! My horse will sometimes come to me, but usually not. It has a lot more to do with how hungry she is and if she has hay in the pasture or not.
A lot of horses also figure out that it doesnt matter if they come up to you or not, either way you're going to walk all the way out there so they might as well wait for you. Most of them get a treat anyway.