I'm no bone expert, but I would think that in using them, most of the good stuff that animals like isn't there anymore by the time they're abandoned.
Its certainly true that fresh bones don't last very long in the wild. That's why not ever finding any bones of the abominable snowman is no proof that he doesn't exist. (Not that I believe he does).
I'm more bewildered why some of these bones survive, yet others don't. Maybe some soil protects, others don't?
We got a little rain here on Wednesday and went back to the same place Thursday. I lost a nice arrowhead by the time I got home, but here is some of the rest of what we found: