Credit unions are not-for-profit- in business primarily to serve their members. If a credit union has excess earnings after reserve requirements are met, those earnings are used to offer the members lower interest on loans or higher interest on savings, to offset costs so as to limit the need for fees, or to develop new products and services for the membership. Excess funds can also be paid back to members as a dividend.
Banks are for-profit, meaning their primary purpose is to generate profits for their stockholders. In banks, only the stockholders-not account holders- get a share of the profits.