Companies, designers and photographers have to wait for users to search for wallpapers on their websites or on websites that collect wallpapers. They cannot know when, who and how many people got their image on their desktop. They can’t direct users from the wallpaper on their desktop to an external URL.
Users have no app to get nice wallpapers of today about personal interests with no efforts. They always have to search for a new one when the old one got extremely boring but searching for a new wallpaper is even more boring. Most of the time they can’t know who is the author of the wallpaper that is on their screen.