Art ...dont even mention it....I have watched certain pieces come back 2 or 3 or 4 times to auction only to skyrocket in price each and every time...its not at all about the look of the art, but just for the value and what the future return will be...if anyone actually believes they are buying a Rothko or picasso because of the way it appeals to them is just a joke. They buy these pieces only as an investment to flip them a decade later for many many multiple tens millions than what they paid.
Applies to collectibles in general too.
One often overlooked "reason" is that art, and other collectibles like wine and watches, are portable. A person can not easily move cash, metals, gems, wtc with regard to the current reporting rules and confiscatory laws. For that matter, a person can not merely get on plane any more! Wait until October 2020 to see the havoc Real ID will cause. But collectibles, they are a different type of safe deposit.
