Please correct me then. After a bank robbery, the notes' serials get marked in a database and when they go out of rotation they are destroyed, the bank gets a new bag of notes and the FDIC assures that whatever happens your money is recovered - through another bank if necessary.
The entire economy is not backed by bullion in a bank's vault, 'losses' in the digital side are simply recovered by rolling back statements. If your account gets hacked and the money is transferred within the country, it can simply be recovered by transferring the money back because all the accounts fall under the same 'governance', even internationally there are some agreements for returning stolen money. If a 'mule' is used, the mule's balance is going to go negative and thus someone, somewhere will be indebted to the banks (whether it is the victim, a mule, the insurance company or the criminal). When insurance companies have to recover the money, they will either get it from the feds or lend the money somewhere (depending on the type of insurance and your jurisdiction - eg. in Europe, a lot of the insurance pools are backed by the government which makes the actual payments)
Cryptocurrency cannot be recovered or re-issued like bank notes can. You cannot have a negative amount of cryptocurrency because it is decentralized and supposedly anonymous. There is no governing agency or international agreement on recovering stolen cryptocurrency, no agency can just issue more currency and subsequently recover it at a later time. There is also a limited supply of them and creating them is costly so it is not feasible to simply have a stash somewhere just for insurance purposes because you would only accelerate the devaluation and instability of the system (if someone holds like 1/3 of a cryptocurrency they can technically 'cheat' the entire system)