Random generation

Why isn't it everywhere? I've talked about biomorphs before, but even without the complicating factor of artificial selection, random generation is very useful. Take, for example, computer games. There are very few computer games, typically the storyline intensive ones, where random generation of levels would not be an added extra for players. Particularly where there's the ability to save and share a randomly generated one that you've tried with other players. Adding random generating extends the playability, making a great game into a classic.