You know, they could have simply done a “Kirk and the Gang - The Early Years” without the alternate timeline twaddle. However, as you noted, that would have prevented Lensflare Abrams from crapifying it with his particular genius. Heck, they could have gone so far as exploring a different aspect of the Trek Universe they way that DS9 and Voyager did, but that would not have allowed Captain Blue Filter to leave his stain, er, mark on established characters.
The reason for the reboot is that the canon of Trek is a giant albatross. Heck just look at all the complaints Enterprise got because they scratched canon once in a while. Nobody wants to drag that crap around. Also if it failed they could have just said “never mind” and gone back into the mud pit. There’s rumors coming out of Paramount about them putting a new show into the old canon universe for the six whiners that can’t handle a reboot.