I found this - https://www.bullionstar.com/blogs/jp-koning/golds-official-p.... The whole article is worth a read, this is the important bit -

“And that is probably why the U.S.’s statutory price of gold stays fixed at a decades-old level of $42.22. The consensus that independent central banking is a good thing (because it keeps a lid on inflation) dictates that the Fed have plenty of ammo. If the official gold price stays at $42.22, the Fed can lay claim to the full 261,498,927 ounces held by the Treasury. If the price is increased, the Fed gets only a sliver of that, the Treasury laying claim to the rest. And with fewer resources, the Fed’s has less control over the purchasing power of currency.”