You may have heard of a country called Myanmar? Population of 54 million?
You might be surprised to learn that a citizen from Myanmar does not have access to a local bank offering USD accounts, nor do they get offers in the mail from Amex or Citibank. Their sole USD option may be holding cash under their mattress.
With a USD stablecoin, this citizen is no longer subject arbitrary exchange rates, expensive banks and risky currency storage. They can save money independently of any government or financial institution.