Ever since ww2 the US military has had a general philosophy of “better to have it and not need it” due to underfunded production and R&D leading up to ww1 and then again during the depression.

Also the only thing rotting in the desert are plastics cause of UV, even cloth will last a decade and a half. Reminder folks’ll put new fluids in a car and it’ll start right up in areas a lot of these tanks are stored. I imagine the same is true for most of the mothballed shit.