Steel Gongs & Shooting...

I was telling some guys at work about my new interest in shooting and somehow the conversation wound its way into shooting at big steel plates.  One of my co-workers told about a 4ft x 8ft x 1/4" thick steel plate that they had hauled out to the middle of some desert in Nevada to shoot at (among other things).  But not wanting to haul the several hundred pounds of steel back out, and since they go to the same place to shoot every year, they just left it there for next year.  Well the next year it was gone.  That's when another co-worker chimed in with "ya just can't leave a good steel gong anywhere!" and he proceeded to tell his own vanishing steel gong story.  So the question is, who is removing these steel gongs so laboriously placed by these shooters?  Is it other shooters?  And if so, why can't they just shoot it right there where it is?  Is it scrap collectors?  If so that is a long way away to go scavenging for scrap metal.  Is it BLM Land Rangers?  If so, what's their beef?