Moving gold across the ocean is expensive. You can only do it so many times before you've expended the full value of the gold. Bitcoin is much easier to move around by comparison.
Keep in mind the vast majority of gold holdings and transactions are between central banks.
I can hand you a piece of gold and the transfer is done. No 74 character address, no keys, no official public ledger of the transaction happening, just a transfer of value between two parties.