Bitcoin's reliance on a functioning internet and power grid renders it significantly more fragile than traditional forms of currency, and relies on a world where these things exist in perpetuity.
This was maybe true when comparing to fiat currencies 60+ years ago, when people were paid in physical cash, kept large amounts of cash at home, paid for everything in cash, wrote checks by hand for larger purchases, banked in person at a branch using paper records, and so on. Now, if the internet and power grid goes out, then fiat will be just as useless as bitcoin. Credit cards won't work. Apple Pay, Google Pay, PayPal, etc., all down. No one can withdraw from an ATM. All online banking and telephone banking offline. Almost all merchants can't ring up your goods, accept payments, or even open the cash register.
That's without touching on the fact that in a scenario of global loss of internet and electricity for any significant length of time, no one will want money. Food, water, fuel, weapons, and medicine will quickly start being traded for each other.