To use an example in another domain, there's a dude named Kevin MacLeod who runs a site called
incompetech – Music and also Graph Paper, where he among other things has a whole lot of royalty-free music available and released under Creative Commons. There are a lot of people who use that music for background in Youtube videos and in other places where some music is needed. Should Kevin decide to "withdraw" certain works, all those videos would suddenly become infringing, and that would mean the license would be pointless.