There needs to be some basic economics here.. Money has value because of the value of the economic transactions in which its conducted. Government-backed currencies are forced to have value in the sense they force people to use it for their taxes. The US, additionally, forces the world to use it for oil trades. Value is in those economic transactions. A currency is just a "liquifying" of that value, to make it easier…
Well obviously, on the superficial level there's plain old greed.
But on a more existential level, bitcoiners are acknowledging that proof of work will lose to proof of lead, in any kind of direct confrontation.
So backing its security with math isn't enough, coiners want it backed with armed force. like fiat.