hmmmm, with such a massive incident (destroying Vulcan) in the timeline, how come the temporal devision of Startrek didnt do something? hell, in the episode 'Relativity' (Voyager) the temporal guys were out to stop just one ship from being destroyed. ...
hmmm got an idea for a script to put things right here
For the same reason they didn't travel back in time to prevent Adm. Janeway from getting VOY home 16 years early.
In my book, they did. It's all a matter of perspective. Audiences get to see the alternate outcomes. The timeline gets still reset by the time cops.
Admiral Janeway appeared in "Star Trek: Nemesis," so that movie continued in the alternate timeline created at the end of "Voyager." And the end of "Voyager" was already set in an alternate timeline created by the Borg in "Star Trek: First Contact," which means the last four Star Trek movies have each taken place in an alternate timeline from the previous movie. This last Trek movie is no different.
These last two Trek movies are a direct continuation of the Borg attack in "Star Trek: First Contact" and the Temporal Cold War in "Star Trek: Enterprise."
(Given enough research, Chris Pine's Kirk could probably locate some records of the Borg attack on Zefram Cochrane two centuries earlier, or the Xindi death ray that wiped out Florida one century earlier. That's assuming that there haven't been a dozen more alternate timelines created in the 100 years since the last episode of "Enterprise.")
Even before Nero showed up, we were already about 17 timelines removed from The Original Series, which itself generated several alternate timelines during its run.
Although people often talk about "restoring" a timeline when history is changed, what they're usually doing is creating a third timeline that more closely resembles the one they prefer.
Sometimes, as in "Endgame" and "Yesterday's Enterprise," the time traveler decides the altered timeline is better than the one they left, and decides to stay there without trying to "restore" it.
Which is the same result of Nero and Spock coming back in time. "Star Trek XI" shows exactly the same temporal mechanics at work as Admiral Janeway in "Endgame" and Lt. Yar in "Yesterday's Enterprise."
They all went into the past, changed the past, and stayed in the past, and none of the alternate timelines they created was ever "restored."