Because unlike gold I can buy stuff with currency....... And I don't know to many people that want to carry around pieces of gold to do their trade. Then of course consumption doesn't satisfy supply. Then there is the anecdotal stories of firms like Goldman driving the price up, and then recently putting on massive shorts.

Then if your really into all that Austrian Non-Theory there are better 'mediums of exchange' like Bitcoin.

To me its a no brainer, you just have to know when the ponzi game is up. Since the large institutions have a heap of shorts on I'm sure they will generate an event that will drive the price down further.