In fact nobody recommends holding one bank account, under any circumstances. Banks can and do freeze accounts for any reason. You always have some backups standing by.
You also don't keep all your assets that way. Businesses can hold reserves in stocks or bonds or gold or cash in a safe just like everyone else.
The VCs didn’t concentrate their money like this for no reason. They got some benefit out of it, surely (easier access to loans for their portfolio companies, I suspect). And VCs are, or should be, sophisticated enough to be accountable for concentrating their capital without purchasing insurance.
There’s no clear way for VCs to pay the price they should pay without some startups being collateral damage. I think that’s the crux of the disagreement about what should have been done.
Founders used SVB because regular banks, if they see you have a failed startup in your history, won't give you a home loan.
Equity holders of three banks just lost all of it - that is exactly what you're asking for.