Because Scrooge McDuck diving into a vault-full of gold is a cartoon and not real. People with wealth generally want to do things with it. Buy yachts, build Casinos, hookers and blow, all that. And that requires a currency that others transact in.

The problem inflationary currency bestows upon capital allocators is insolvable. They are given money of no certain value (pretty much the only sure thing about the paper currency is that it is, literally, burning in your hands, it ticks away like a bomb, it blows in the wind like dust - all this while you're holding it) and have to do something with it. They always, always, always, absolutely always have more than is in fact needed.