Wasn't Lyse poorly received by a lot of people who were mad about the whole Yda identity thing? Plus she just had a whole expansion where she was a major focus. That's the real world reason.
In game story reason has been pointed out, but another thing to consider, though it's already been alluded to, is that the Exarch knows of our future since he wants to prevent the Calamity that he's already lived through. The way I look at it, is he called over everyone that had a similar happenstance in regards to their death in that Calamity.
I took it as, all of the Scions who got called were warriors who were killed by Black Rose in that timeline, like the WoL. This would explain why they're similar enough to who he is trying to call, in order for them to be mistakenly snatched.