Cash or a bank demand account is not without their own inherent risks. A fire, robbery, or forced currency exchange could destroy the value of the physical commodity of cash, and the FDIC only insures individual account bank deposits up to a certain limit so a bank institution failure could cause losses to individual accounts.
Ok you're arguing that there is no such thing as a liquid store of value that that offers a better return than a negative yield government bond?
So let's say I'm a bank with a stack of 1B in high denomination central bank notes. I calculate the rate of return as zero minus the annual cost of securing those and the annual risk that they are stolen or destroyed. Inflation isn't a factor because the bond is in the same currency. Based on your explanation that rate of return will be lower than the -0.11% that I would get from a german 30 year bond today. And there's simply nothing I can exchange those central bank notes for that would do any better than the bond.
Like OP I've never understood negative yield debt and I'm trying really hard to.
