I have worked at an independent RIA for a little over a year now, and I can tell first hand that banks are not suited to manage accounts even reaching in to the millions. The larger the bank, the less personal service you receive. To get decent service from a bank, an account may have to have over $10,000,000. High fees are a hallmark of any wealth management bank.
While many people with smaller account may choose to manage their own accounts, essentially for free, most people can benefit from the advice and management of a professional. With banks focusing on larger revenue clients, independent RIAs fill an important gap that the vast majority of savers occupy.