Major successes...are Avatar, Star Wars, DarkKight to which no Trek Film has come remotely close to.
I think the thing you're missing is the fact that Star Trek is a 'bankable' project. Anytime the studio commits money to a Trek film... it knows that it will be receiving a return on its' investment. Even on Treks' darkest night (Enterprise and Star Trek: Nemesis), Paramount profited.
Now ask a studio executive which one he'd rather bankroll:
Make a Star Trek flick with a smallish investment and guaranteed $20 - $30 million dollar return.
-or-
Gamble $400 million on an 'unknown' film that general audiences may or may not take a liking too. Yeah it may hit it big... then again it may bankrupt your studio.