Why did the world need to end for the Fears to spread?

Edit: answers so far:

1. My own, in the tags. It would force Jon to make that decision when put in the impossible position of the finale.

2. Also my own. No one could have done it, not even Jon, before the apocalypse? Maybe? (Because he wasn’t a proper archive yet.) Both my theories are a little shaky.

3. via annabelle–cane: Annabelle (the, uh, the ‘real’ one…you get what I mean) does say this:

“Oh, it’s so much more than a crack now. It’s an aching hole, a gaping wound in the very fabric of our world.” (MAG 196)

and in the actual statement in 196 there’s this: “It was not wide enough to allow true passage, not yet, save for the odd accident. But it was wide enough for what we now intended…”

implying that the crack only widened enough after the world ended, because everything got Mega Spooky.

4. via gammija: the Fears needed to come into our world first and then go to others. Also they’re more vulnerable here, so killing the Pupil would only then (when they’re on Earth) untether them and enable them to spread.