The Google team responds with the following
Your app does not contain a full-size app banner or is it not visible in the launcher. We are targeting 1080P, which we consider xhdpi. Apps should include the banner in the xhdpi (320 dpi) drawables folder with a size of (320px × 180px). Please refer to our Home Screen Banner and UI Patterns documentation.
The title should help users identify apps in the launcher. Please refer to our Visual Design and User Interaction documentation for more information.
For example, your banner does not fill the entire banner space.