They make profit more often than loss. I agree banks in UK suck but at least big banks will always be bailed out by government in case they were in too much trouble, see last financial crises.
A private startup running on VC money would not be bailed out in such case and be allowed to fail. I know that up to 85k of my money is in theory insured and I would get it back.
But it’s still better to derisk so I don’t have to deal with that process in case of financial calamity (it would probably be very stressful process to go through the bureaucracy to get your FSCS insured money back and might take weeks or months).