Does every hero banner need a call to action?

No, but the hero should always help the visitor understand what to do next. A lead-generation page usually needs a primary conversion action such as scheduling a consultation or requesting information. A homepage may use a primary action plus a navigational option for visitors who are still exploring, while a portfolio or brand page may guide people into the content before asking for a commitment. Match the action to the page's purpose instead of adding a button by habit.