Gold has some intrinsic value (you can make stuff out of it at least). Same for makeshift currencies like the Tide detergent.
US dollars are backed by US industrial and military power.
Random crypto tokens have about as much value as paper money: they are relatively hard to produce, but not very much so. They need to be backed by a power / reputation of some kind, or a directly consumable resource of some kind, to be widely usable.
If the USD has $1TT stolen or an anti-counterfeit measure is bypassed, the US government could step in and support use of the dollar with some guarantee or security advancement like better counterfeiting protections or freezing stolen assets then (as bad as it is often seen) printing replacement bills or something. Some of this is already ongoing with the Mint developing anti-counterfeit measures for each new bill released.
Crypto can't do that, it's just a volatile stock like commodity with no underwritten assets or real world backing. There's no centralized backer that can prop it up in crisis. That's risky.
Not only that, but all these self-cryptos would be backed by the word of the person, and people lie, so you could potentially just end up with a whole bunch of crypto coins worth nothing in the end.