Option for Decommissioning an (Exhausted) World Map mines.

On the Wiki there is information that you can upgrade your "External" Mines(especially the Oil rigs) up to Lvl 16 but in reality such investing of monstrous amounts of building materials usually never happens, unless you play on a lighter difficulties or have the "Unlimited" setting of World mape resources. And once those mines get completely exhausted they just idly sit there, draining unity(unless you disable them immediately),
So why we cant' just tear those now uselesss structures down for either building materials or recyclables?