Replacing the rusted gas tank in my Miata...How does this happen?

In todays video I had to remove the subframe among other things like the driveshaft, brake lines, speed sensor, hand brake, rear suspension etc. All of this had to be done in order to replace a rusted gas tank. I don't know how this happens but I guess its a thing for miata's. Unfortunately i didn't record me putting it back together :(