Samuel L. Jackson knows that he's cashing a check and not making a Scorsese film, so why should the studio signing his check try and dress up a perfectly good snakes-on-a-plane flick with a stupid title like Pacific Air Flight 121? From Collider.com:
Beaks: One of those films that you’re working on right now is... well, it’s called Pacific Air 121—
Jackson: Snakes on a Plane, man!
Jackson: We’re totally changing that back. That’s the only reason I took the job: I read the title.
Beaks: Snakes on a Plane! That’s everything!
Jackson: You either want to see that, or you don’t.
Beaks: And how are those snakes? Besides being on a plane?
Jackson: Some of them are aggressive, some of them are cool. They’re interesting to watch, and interesting to interact with. It depends on what kind of snake it is. One day, it took, like, four guys to bring in this 350 lb. Burmese Python. We were all like, “Where’s that goin’?” And I watched an Albino Cobra strike airplane seats the other day. I watched it from another studio. It’s actually been a fun show. But we’re taking the name back!
Seriously, though. Snakes on a Plane is probably the best title for a movie that we've ever heard. We'll even lend them a tagline for the one-sheet, should they decide to ride this one all the way to first place: "Anacondas on land are for pussies. SNAKES ON A PLANE!"