That's because Hollywood is lame. Out of every 50 movies greenlighted, there might be three or four that are truly worth anything, and are actually unique and meaningful and stand on their own as just a great story.
The other 47 or so are just shit-awful exercises in stunt-casting, sequel idiocy, trendy rip-offs, the aforementioned video game/cartoon adaptations (which always, always suck), manipulative "feel good" crap, retreads, remakes, A-list ego projects, two hours of Meg Ryan scrunching her nose, unfunny four-minute SNL sketches made into REALLY unfunny 90 minute feature films, teen angst dramas with Freddie Prinze, Jr., mismatched "buddy movies", desperate men who "fights the system to clear his name and save the woman he loves", sappy road trip movies where put-upon women discover themselves and drive with the top down to a Carly Simon song, etc.
Did I leave anything out?