Gold is a store of value. Stores of value provide a useful function in society. Very few things actually qualify as stores of value, and gold is the most known of them so I used that, but you could replace the string 'gold' with 'store of value' in my argument without changing the substance of my argument.
Something is a store of value because you expect that other people will value it as highly in the future as they do now. (Or at least some predictable fraction less, accounting for inflation.) Whether it's gold or dollars, it's still based on investor psychology, and is still just as subject to whims of herd behavior. Ask people who bought gold in 1979 how well it stored its value.