It's not but its a lot easier and safer to hold digital currency than wads of cash in your floorboards. Easier to acquire, receive from abroad and verify as well. It allows for a form of civil disobedience against unjust laws
You can print out a seed phrase and hold it under your floorboards as well, or better yet, memorize it. It takes up less space. You can split the phrase up and give it to a few trusted parties. You can do multi-sig. It's easier to transport, etc etc etc
Various weights of gold or silver are the better comparison versus wads of cash, but your point is taken since I guess the completely digital acquisition is the difference.