So... someone actually went to the trouble of burying a bunch of games in the desert and then kept the location a secret? That part of the myth always made me think, "wait, what?". Buried in a secret remote location sounds like the origin of a cursed ancient artifact or a horror monster. How on earth do you go from, "our game isn't selling," to, "bury them where no mortal shall ever find them"?
Well, the missing steps to bring this back to realism is a long chain of "not in my backyard!"
Works for me.
They had millions of cartridges that were worthless as their business was crumbling and going into bankruptcy. They couldn't sell them. They couldn't write them off. How else do you get rid of that much worthless stock?
I still can't help but think that they were going to more trouble than was necessary. Just always sounded odd to me is all.
Recycling?
No way to "recycle" the carts (i.e. put a different game program and labels on them) because of the sheer number of cartridges and the falling market for them. Shredding and meltdown would have been VERY expensive and messy. Burial was the easiest way to get rid of them.