Why do people want movies based on video games?

What happens to video games based on movies for the most part?  Don't they all suck, haven't they all dissappoint.  But every time we get a fake Halo movie update the nerds and noobs collectively release in their pants.  Shouldn't we have learned from the last 20 years of hollywood trying to capitalize on video games.  They are probably rolling on the ground laughing literally.  They can make it as bad as they want and it will make $200 million domestically easily.  They will say they are getting some underground director, are working intensely on a script, but do they really care?  It's the same principle of video games based on the movies. 

I really can't understand the reason for this.  Oh I get your a huge fan boy, you love Halo, you have all 20 or whatever actually video games, the hundreds of additional maps you need to fucking buy.  You've probably spent a good $3000 on the whole halo experience since Day 1.  Which is precisely the point of why I don't know the reason fanboys love this shit.  It's not like Mario Bros, Double Dragon, or Street Fighter that essentially have no story, you've spent hours (days) immersing yourself completely in this world.  A world filled with characters, action, compelling story, fantastic effects that you get to interact with, and now you are willing to pay opening day ticket prices hand over fist to watch a 1 hour 50 minute movie that will probably explore everything you already know about the story because they want to include the people who don't play the halo games, keep them up to date and ready for the sequel.  Have people played a video game recently?  That is all it is.  You have this completely immersive experience, what technology is ultimately going for, and you take a evolutionary step back, jack up the price, and get pissed off about it after you see it and bitch on message boards over how much it sucked. 

I guess it makes you want to play the game more but in comparison it is like having a teleporter and having a car.  obviously you are are still going to use the car but you aren't going to drive somewhere if you can teleport there with no problem.  The same could be said in that case of the vintage value of going to see a movie, but do you really think interacting in a complete world of fiction and living your life in there  can even compare to a PG-13 summer tentpole watered down mung?

Oh and you are excited for the Bioshock movie rumors too?