If the enemy acted the same way I expected, then they'd never have plans or countermeasures for such a crazy move.
After all who was in their right mind would give away his defences to the enemy and retreat all the way back to the centre?
So the enemy would think that I planned to flee from here and was trying to cut down my losses.
If they followed through this line of thoughts, then they'd end up following the same plan and tactic they were currently using.
One race was using their minds and the other wasn't. So if my forces ran without caring for anything else, this entire war would turn into a marathon between the two sides!
That locust race would keep following my forces like mad dogs. As for the Silence race, they wouldn't be able to keep up with the speed of my side and their locust forces.
Even if at some point they felt something was amiss, it'd be too late to try and stop the far away locust race.