I'm surprised too that more people don't do this. I think probably just out of habit/tradition.
The reason why not everyone goes through bales of hay quickly (meaning, into the wheelbarrow, and gone in a few minutes) is because many of us only have between one and say, 2 or 3 horses. In bigger barns, sure, an open bale of hay is distributed completely once opened.
We have 2 horses in our barn, and the vertical storage has turned out to be great because one of the horses will only eat the freshest hay... if it was a flake that had been lying over accordion style, he would pick at it.
"I have never let my schooling interfere with my education." - Mark Twain