I'm going to make an assumption. You circled Background Photo ON, in Glance Screen app, which I believe you are questioning why not have the Background Photo appear in the background of screens, especially those "ugly" with blank space.
I too would like this, however many backgrounds I use and like as my Start screen and Lock screen are AWFUL for viewing white text whether stationary or scrolling. I'm using bright Autumn images now with light browns, oranges and yellows. White text is hard to see. I use a weather app who's text is almost impossible to see at times when the app is open and certain within app backgrounds are used depending on time of day and current weather. The photos are beautiful, but data is very hard to read sometimes. Same for the OS itself depending on a users background photo.
I don't like that White is the only color of tile icons, with the exception of some apps that don't offer transparent tiles. It would be nice if the OS could determine a text and icon color that best contrasted the overall background image thus offering the best legibility, but for now it's white (dark mode, High Contrast mode off).