I've always thought that the issue is that if Bella had more of a personality and was more reactive it would ruin the rest of the storyline. A personality would mandate some kind of sensible reaction to being stalked non-stop by supernatural weirdos, and especilly early on any kind of realistic reaction to the situation would have ruined the entire story. Any real personality that could be made to react according to the needs of the plotline would come accross as being totally dysfunctional to the point of making projection by the reader impossible.
There have been tons of things written about how creepy a lot of Edward's behaviors are, and yet nobody notices. By this I don't mean the vampire "creepy" bits, I mean the kinds of behavior that even for a non-Vampire would warrent a restraining order even if the guy was Adonis.
-
That said, I think the whole thing being so weak in implausible to any rational thought is why it was chosen by the powers that be in Hollywood and so on to be face of "Paranormal Romance" that they were going to promote. The entire work is objectively terrible and impossible to take seriously.
Now loon back at situations with similar kinds of material like the "Vampire The Masquerade" RPG, or other, better constructed universes and lore systems that acheived fanatical followings. A concern being people taking it too seriously, or being manipulated through obsession, which would generate the wrong kind of contreversy and bring their long-term franchise potential to a premature end.
Think of situations like
http://roswell.fortunecity.com/seance/500/killers/family.html
http://www.karisable.com/ymvamp.htm
There was also a case when "Vampire: The Masquerade" was newer where, there was a (non murderous) teenage sex scandal involving teachers at a school manipulating students through the RPG group and the like.
The bottom line here is that "Twilight" just doesn't have the kind of mythology behind it where Hollywood would expect it to create the kind of obessesive detachment from reality that has hurt other franchises, and with the somewhat touchy history of fantasy vampire lore, exploiting the fad was probably akin to walking a tightrope, because with time you could dig out a bunch of stories about wierd Vampire fans (RPG and otherwise). Heck, "Something Awful" even did articles mocking sites where people who allegedly think they are real Vampires go to hang out and talk about Vampire stuff.
"Twilight", "True Blood", and similar franchises all share the simple trait in common that they are impossible to take seriously. Notice that just between those two series Bella and Sookie have a lot in common.... both being complete morons in reaction to what's going on. What's more neither is remotely believable, in one universe we've got Vampires who sparkle (and truthfully in "Twilight" I don't really 'get' the downside of being a Vampire, and why they wouldn't turn someone they care about), in "True Blood" we're supposed to believe that the authorities let Vampires kick around publically, doing whatever the heck they want, up to and including maintaining their own seperate justice system. One would think that as part of such acceptance would have been the development of squads in law enforcement trained to exploit their weaknesses when they step out of line (in that universe at least the Vampires do have signifigant weaknesses). Of course the whole mystique would be ruined if some Vampire Sheriff/Crime Lord wound up getting slammed into the back of a keyboard on "Cops: The Redneck South" to the tune of "Bad Boys" and then chained up with silver permanantly inside of a cell with his new buddy "Bubba".
All of the big vampire franchises right now have "not making one bit of sense when you think about them" in common, and I think it's internaionally set up that way by the people producing them.