Aircraft aluminum can sit in the jungle for thirty years -- hell, fifty years -- and still look like a plane.
If there's not a lot of wreckage in one spot, that only means it's spread over a wide area.
There's no wildlife that eats aluminum, corrosion is pretty much not a factor, and that leaves only the original crash vectors and weather as factors.
It's all there. It's just that "there" may be a whole lot of acres.
