But if you're a midsized construction firm turning over $10 million a month 40 bank accounts is unwieldy. If you're that and watch SVB collapse with the slow pokes holding the bag then you move to one of the big 4. For a few reasons:
(1) SVB taught you that the feds will let a bank run happen
(2) They won't save the poor saps that were too slow moving their money
(3) The systemically important banks are too big to fail. A bank that can't pay depositors back is failed. Ergo, the SIB are too big to lose customer deposits.
So you flee your regional bank because the single most important thing about a bank is that they don't lose your money.