I used to think the same thing, but it's not about putting the gold bar in a large empty room. Consider that the our galaxy has a mass of about 6×10^42 kg. The relative abundance of gold is 6×10^-10, so our galaxy has 4×10^33 kg of gold.

The gold bar isn't in a large empty room. It's in a room filled with piles of gold, each more massive than the planet Mercury, for every person on Earth. Amongst those piles, would that single bar still hold value to you?

Edit: Formatting engine didn't like using * for multiplication