This allows Brex to capture card transaction fees from financial services other banks ignore (again, due to risk models), such as startup charge cards.
For how many businesses is "a charge card for 15% of your cash balance and you're responsible for fraud" substantively different from just using a debit card? (Genuine question -- this isn't a market I realized even exists.)
I’d probably still go with Amex corporate cards and a personal guarantee, based on personal preference, a deep credit file, and a desire to outsource spend exception handling to the bank.
I think the reason large banks haven’t offered this yet is they’re not very catered to startups, which might have a large balance but no credit history (either as a business, or because the founders are young or foreign).
(My company somewhat competes with Brex cash but doesn’t offer a charge card or credit card product)