The odds that 100% of businesses each decide to pull their money out of the same bank at the same time is less than 1% of businesses who invested at the same bank pulling out their money. Especially if they are in the same industry and know the same people urging a sudden withdrawal. Maybe even mostly located in the same geographic region.
But if the FDIC insures all deposits anyway, then there would never be a bank run to begin with because nobody would panic that they wouldn't get their money out, so spreading risk among multiple banks is a "solution" to an artificial problem.
It's a solution to a bank run because of fear of the banks going under. It's not a solution to a bank run because an industry needs cash quickly. For instance, Silvergate had a lot of crypto firms as clients, and in late 2022/early 2023 all those clients needed cash. You can imagine something similar happening in other industries.
I don't see a problem with a rule or regulation that limits individual daily withdrawal limits. That would solve that specific issue as well, and anybody who needs to withdraw more than that per day clearly has enough funds to have accountants that can coordinate across multiple banks.
