I am so tired of the wallpapers I like being removed from my choices. What is the problem? Not enough storage? I'm baffled as to why I can't use any wallpaper I have used in the past, but have a lot of really lame ones to choose from now.
Could be the copyright to those photos was changed and stated Google/the manufacturer couldn't include them anymore. Or it could be that the particular phone you have, has each update themed with a set of skins and wallpaper.
If you'd like them back, the Internet has a great archive of said photos. Just use your favorite search engine to search up "Stock Wallpapers <insert your phone model here>"