Moreover, couldn't they just have uh... made a story that doesn't require knowledge of continuity to understand instead of erasing all the continuity?.
Think of it as tearing off the bandaid in one fell swoop rather than suffering a dozen little stings and winces. Once you decide you want a fresh start, it's better to dispose of all the old "canon" quickly and efficiently rather than subject your new cycle of TREK movies to years of nitpicking and plot constraints . . . .
("But wait, Kirk can't meet the Borg now. That never happened in the original timeline. Canon violation!")
Now they have a clean slate to work with . . .