In order to pay their bills, Chess.com either has to allow adds or else charge a membership fee to all of its members. Imagine the outrage if Chess.com suddenly said "no more free memberships".
Anyone who wants to avoid the adds should sign up for a premium membership.
Their integrety for running a site that costs them money so they are trying to defray some of their costs? Sure, some sites run completely free without any ads but not all do. If the business model isn't working, it will change or the site will lose customers.