Administering a checking account is not cost-less. Looks like SIVB’s return on assets is 1.87% [1] implying $467 of annual revenue for the account at $25k average balance. This is probably more or less break-even (maybe it’s $200?) - point being is they lose money on small accounts...
[1] https://finance.yahoo.com/quote/SIVB/key-statistics?p=SIVB