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.