And lots of local businesses. 100 employees at 48k a year gets you to 200k a month in payroll. Never mind the money it takes to run that business.
Even if you are under the 250k mark, if your bank closes on a pay day your staff is the group that suffers.
The specific problem for SVB was that many VCs got their companies to agree not to do this, specifically to keep all the money in SVB.
What was in it for the VCs???
I work for a six-person startup; our CEO landed on Brex after SVB, and one of the reasons he gave was that it does exactly this (up to 9 banks). See https://www.brex.com/product/business-account