Cause it's product, and you don't make money by pissing off 90% of your audience. And no, it doesn't matter that it's the last film. And no, it doesn't matter that Nolan's made WB billions already.
I will say, with 100% certainty, that WB would not allow Christopher Nolan to kill of Bruce Wayne.
Nolan has quite a bit control, and from the rumors where this started, WB was originally pissed about the ending, and they have said now they will reboot it.
And people won't be pissed off if the story wraps up well, I'm glad Nolan who has great imagination is writing it, because there are many ways to go about it where the audience will feel alright with the heroes death. If the actions of his death have greater purpose then it works. Like Spock said as he dies, the needs of the many outweigh the needs of the few. You are just jumping to the conclusion that it would not be a hopeful ending with Batman dead, I guarantee (especially since Nolan is a master with endings) there will be a good hopeful feeling, but I'm sure it will be bittersweet, it worked for Cobb in Inception.
Sorry, final cut or not, if you don't think that there are SOME parameters, you're crazy.
First of all, the film must be PG-13. That's a mandate right there.
People die all the time in PG-13 movies that is a moot point.
I understand your meaning and agree in principle so please forgive me for using this extract as a jumping off point as where I'm going next is only tangentially related.
Anyhoo... Armageddon. Not the one due in 2012, the one with Bruce Willis in it. We all know how it ends, the hero triggers something that saves the day. And as tragic an ending as that was, no one left the theater with the idea of having Stamper survive to fight another day. The sacrifice was made. The world was saved. The End. And therein lies the difference: The general audienceand most devotees of the charactershould they have just witnessed the death of an icon will not be able to leave the theater without desperately wishing that Batman had survived to fight another day. That's what the audience wants to believe will happen once the credits rollthat in that imaginary world Batman is still there fighting evildoers. This doesn't mean Nolan can't kill off Batman, but if he does its all but certain to leave things on a sour note and the only thing killing off this Batman will achieve is ending Nolan's trilogy. It will not end Batman nor prevent other Batman films from being made and as a result Nolan's trilogy will be relegated to something other and not part of the overall mythology. Batmanand Bruce Waynelive it that mythology and killing off Batman/Wayne unequivocally takes this trilogy out of that stream.
He will, his legacy will live on, people like Catwoman, and the possibility of a second generation (like in the comics with Robin/Nightwing or Jean-Paul before he went bad) will continue his legacy, and just like Terry in Batman Beyond. Bruce can't do it forever he's a man, and the general audience knows this and has accepted the illusion of this being a more real world feel. They know he's mortal. But his symbol is not, he could continue to inspire people to do the right thing, that is what Batman stands for. If Gotham ends up fighting for themselves and breeding new people in the shadow of the Bat, then the audience will leave feeling like Armageddon, only much better because it was a terrible movie lol.
I honestly don't know what will happen, I think death/non-death could both be as powerful and work in many ways. We just can't look at one instance how it could go, Nolan is unpredictable, he though always makes the most powerful endings. That is his gift.