With cash, they can only do it to everybody at once or not at all. With a number in a bank's database, they can selectively expropriate people based on any crit

With cash, they can only do it to everybody at once or not at all. With a number in a bank's database, they can selectively expropriate people based on any criterion with as little effort as between zero (in the case of tacit understanding) and a dozen (if they have to remind the banks that a tax audit is technically overdue or something) phone calls.