Forgive the naive question, but why did so many companies put all their cash in one account instead of spreading it between two or more independent banks?
Large companies and smart individuals keep cash reserves in pass-thru depository products like CDARS which do exactly what you describe. You have a virtual account at Bank A that shows your balance, but the actual money is stored across hundreds or thousands of other banks across the US - each holding less than the FDIC insurance maximum.
I guess if someone loans you money, they want to be able to keep an eye on any sudden moves you make with it.
I'm curious about the calculus that makes this tradeoff non-worthwhile when it comes to squirreling away an emergency payroll fund in a backup bank. What about that is unmanageable?