You know you can change your course mid travel, right? You can picture it like Dragonball Z Abridged Episode 30 Part 2, 2:13:
I not understood this reference, sorry ¯\_(ツ)_/¯ Not familiar with Dragonballz series
I meant that even when The Scourge can't
conquer eat the galaxy due to its dwellers, The Scourge
still refuses to cooperate in beating those "hunters".
Look at it from the lore view. Via communication with The Scourge, we could learn what they escaping from some the "hunters", they are in desperate. In order to keep moving, they rushing through galaxies, eating everything in the way, because w/o this feeding they can't go to another galaxy. So, desperate rushing meaning there can't be scouts, this is just avant-guard before everything else. Once they moved forward, they can't go back or change the course.
Well, -if- there are scouts w/ main forces waiting for good news or capable to change the course, this doesn't change the next thing.
When The Scourge facing someone strong enough to kill The Scourge or at least to hold them back, meaning The Scourge stuck in the galaxy, they still refusing to cooperate, even if locals proposing their help.
So, ultimately, The Scourge rather will die, than try and pick some help and finally get rid of the "hunters". They are developed enough to roam from galaxy to galaxy, but aren't to change or add something to their strategy. Weird, IMO.