Changing cover/poster art for rereleases of old movies.
I'm even seeing it with some all time great posters. Rosemary's Baby's poster is brilliant, really captured the at times nightmarish, paranoid atmosphere of the movie, but they changed it to something bland and modern. For Aliens recent 4k release they just used a still from the movie and touched it up.
I suppose they do this to make the packaging more modern, but most modern poster art sucks.