Why do cryptocurrency proponents bring up negative interest rates as a problem of conventional central banking?

“Hard” assets like gold and BTC by definition can’t be used for fractional reserve banking and instead must be warehoused (or you bury your good in the back yard and hope nobody steals it). Hence yiu are typically paying someone to warehouse your gold (there’s a fair amount of literature on this) or paying for a public wallet, rather than having the bank pay you. How is that any different from paying he central bank to sell you a bond?