It's very simple: those two are not the same media. A movie, a book are made to tell a story. A video game is made for playing, not for telling a story. They should stop adapting video games, it's pointless.
Lots of games tell stories these days. There's no fundamental reason those stories couldn't be adopted to the silver screen. Of course many of these stories aren't really very good, but the same can also be said of any medium. There are elements that might not translate, but that's true of any adaptation. For instance Bioshock's infamous "Would you kindly" plot point won't come though the same way in a movie.