Not sure what you mean... banks definitely have to worry about people unexpectedly coming and asking for all their money back [1]. The difference is, that risk management is the bank's core business. That's not the business Anthropic wants to be in.

[1] https://en.wikipedia.org/wiki/Bank_run

Banks have very strict legal rules about minimum balance sheets. They don't have to have 100% coverage, but that doesn't mean it isn't there.