Then they release it to users who have control over their devices and can modify how their device displays the app. Users are under no obligation to ensure that the app runs as-designed, and if it's not explicitly disallowed they should be free to modify how the app runs. They could modify it to show another language, or put tape over part of the screen to hide some content, or they could download a tool that modifies their hosts file to alter how the app runs.

Point being, you can't count on ads being shown to all of your users as you can't guarantee control over their devices. If you don't like that, then don't make apps that rely on ad revenue.