Supply and demand.

These sell for 8 keys without a doubt.

They rarely get less than 20 ref.

It's a sweet hat, and used as currency.

This hat originates from preordering a $50 game, the fact that its not worth $50 is reassuring that the economy isn't totally insane.

It's a stable valued hat with constant and even supply and demand, so it found a niche as a stable form of currency @8 keys +1-2 given paint. While they can be found slightly cheaper and can always be found slightly more expensive (outpost overpricing), 8 keys is accepted as being fair. That being said, the price of keys varies, so the price of this hat also varies as such. This hat takes into account 1 key is 2.55; if keys change in general value so will this, more or less.

Its been a old currency.

They're EASILY sold at 20 ref, even above some time. Used as a currency, and it's unobtainable now, so the number of them in circulation are only going to decrease.

It's currency, it's not subjective and quantity isn't a factor.

Looks good too, on top of as currency, everyone accepts them in trades, especially higher-valued trades as sweeteners.