Because just providing config options for text and background wouldn't be enough. Most apps use more colors than just background/foreground, meaning those other

Because just providing config options for text and background wouldn't be enough. Most apps use more colors than just background/foreground, meaning those other colors should be configurable as well. Allowing users to configure all colors, would be in conflict with apps that use colors as part of some brand identity and for apps where this wouldn't be an issue, I guess most developers decide providing complete customization of colors is not worth the extra development time.