Any large bureaucracy has standards for loan/lending evaluation. Inevitably those standards become more and more restrictive and conservative, because of risk management.
Private businesses are willing to take on more risk to reach different segments of a market.
As an example, take SVB. One of SVB's markets are startups: companies with no track record, spotty revenues, large and non-repeating transactions, and fluid ownership. A normal bank would consider a startup a money-laundering operation: no visible sources of income, with really large incoming and outgoing transactions that happen intermittently. Many startups also do business internationally, which is another huge red flag for normal banks.
This makes a regular bank much, much slower. Normal banks will put holds on financial transfers because of...risk management. SVB didn't, because that's their "normal."
It's the same for underserved/unbanked (ie: poor) communities. Lending standards have to be different because the community is different. In fact, the new wave of FinTech places are experimenting with other ways of judging creditworthiness, which would be very difficult or impossible to do in a large institution because of...you guessed it, risk management().
It's the same with private businesses vs public businesses. Why not just have a Wal-Mart run by the state? Oh, because every new vendor somehow will need to scale out massively to sell a product...which is probably impossible, both financially and logistically.
Is it possible to design a bureaucratic structure that is both all-encompassing and flexible? Probably...but in the (albeit short) history of bureaucracy it hasn't been done successfully.
() these small fintechs eventually get bought by the big players if the tech proves out