How do you reboot the franchise and wipe out the entire 43-year continuity of five entire series of hundreds of episodes and ten movies (not to mention the thousands of books), without "alienating all the fans by tossing aside the well-loved and already established content"? You can't.
They pretty much have to. They can't maintain continuity with an old series with actors being old or dead. They're not having much success creating a new series.
Here are basically their choices:
Try to start a new series. They haven't had that much luck with that recently.
Kill Star Trek permanently. They've gotten very close to this, but so many people like Star Trek that it makes sense to try to continue it.
Try to resurrect an old series by performing a reboot.
Make more movies.
Option #4 they tried, but they're running out of ways to make movies:
Making a movie out of TOS is out of the question. Some of the actors are dead, and most are way too old. Leonard can't even play Spock anymore - he has to play his father or older version of himself.
TNG has some of the same issues. The actors are still alive, but most are getting way too old, especially Brent Spiner, who has to portray android that doesn't age. I'm surprised he allowed them to bring in B4 in the last movie.
The other series just don't look like they'd make good movies, and don't have quite the fanbase of the first two series.
They basically chose option #3, and they chose to reboot TOS. Only time will tell if they're just gonna make more movies (I hope not) or make a TV series out of it.
Maybe TNG would have been a better choice to reboot? Perhaps. But I guess they made their decision.
FYI, piece of trivia: The computer's voice is played by Majel Barrett-Roddenberry, and she's played a role in every Star Trek series and most of the movies, including playing the computer's voice in the new movie. Unfortunately, she's gone now, so somebody else has to play the computer's voice in any new Star Trek stuff.
Here's my issue with what they did.
They could have created a reboot without erasing any continuity, without needing any alternate universe explanation (it might mess with 'Future Trek' scenes but that would be it) if they placed it in the 25th century. They could have had a brand new ship, a brand new crew, a brand new idea (exploring another galaxy, [insert power here] becoming friendly (like XI), etc.)... They would only have to keep a few things constant: the overall setting and theme.
They kept the setting the same (at least, they didn't do anything overtly changing it). Whether they kept the theme the same is subject to debate in this thread. I don't think they did a good job of it if they tried.
But instead, they chose to do a prequel story. They tried to keep the theme, setting, and characters the same. And I don't think they kept the characters the same well either. (Despite Abrams words that the movie is 'about characters', I agree with people who say these aren't the TOS characters.)
But again, why is this necessary? If Abrams truly wanted to put a new face on Star Trek, why do what he did? Why not start all over again, like TNG? Granted, TNG was done by the same people who produced the last TOS movies. But they recognized Kirk and co. were getting old and so went ahead into the Trek universe, exploring more of it via a 100 year jump into the future.
What I'm getting at is that they could have made the movie a reboot and a starting point for a new series and not mess with continuity any more than any other movie did and keep the plot the same. Spock and Nero could have travelled to the future instead of the past. They could have done the exact same plotline, just with a different crew and ship in the future.
