The problem is, once a company has been there done that, they have to try and come up with something new. As we adapt to the game styles, we can beat games quicker than before. Now that isn't to say the game companys haven't been getting lazy.
A perfect example is Duke Nukem. A game that could have been great if they released it when they were using the Quake 2 engine. They had the storyline, and most of it done, but then worried that the engine wasn't the way to go because it wasn't the latest and greatest. Look where they are now.