Originally Posted by
Darian[Supercell]
There are several reasons we don't want to implement something like this. Like with all things, there's a trade off. While it does provide you with more control over how much loot you withdraw from your treasury, ultimately it would be detrimental to the game's economy. Keeping your treasury loot THAT secure would reduce the amount of available loot for attackers.
When you withdraw loot from the Treasury for a specific purpose, say you need Gold for an upgrade, the Elixir and Dark Elixir that gets withdrawn adds to the pool of available loot for other players when they attack you. This keeps the in-game economy moving.