What problem does this address?

I am receiving support questions related to block themes, and one of the questions that has been recurring is how to add a body background image without access to the Customizer.

This is possible using the cover block. But if you want to use the same background image on all pages on the site, you need to add the block to all the templates.
In my opinion, the cover block is superior to the body background image settings that is available in the customizer, except for in this scenario, because of the effort it takes to add the image to all templates.

What is your proposed solution?

I am suggesting that a site wide body background image option could be added to the styles sidebar.

Related: #16479