My WWII Marine father saw the same when leaving the Marshall Islands at the end of the war. Jeeps, trucks,
airplanes & other equipment were dropped in the ocean just beyond the reef.
He was told the US manufacturers were promised nothing would come back at war’s end so the post war economy would not be depressed by military surplus in the marketplace.
There was a huge domestic surplus market after the war. It must have been all the materiel that never got sent into theater.
Nearly all the Navy’s PT boats were burned in place in the South Pacific. I saw a movie as a kid about smugglers using PT craft for gunrunning. Their extreme speed made them ideal for the role. I remember pics in magazines of combat aircraft being melted down for the aluminum.
What’s happening with equipment in Afghanistan is outrageous, it should all be destroyed in place or else Karzai & his band of crooks will sell/give it to the Taliban.