The character this was supposed to be was not specified when he got the task. The only specification regarding the deco was that the trailer should be silver. As you can read below, the designer was guided by the material of the mold. So, with Laser Prime (who is the main use of this mold), both the alt mode windows and robot mode chest windows are made of clear plastic which is a departure from the original toy. Since the clear plastic for "Scourge" is pink, that means the entire robot mode torso would also be pink clear plastic. This mold was designed so that the torso clear plastic would match the alt mode clear plastic. So, when it came time to decide the colour of the torso, black was chosen for the torso to match the alt mode accordingly.
So there you go, it seems to all come back from a lack of unified direction for the deco and character at the beginning as well as limitations from the way the Legacy Laser Prime mold is constructed.
The designer does conclude that despite all that (limitations and lack of clarity) he went with the best looking deco he could think of. On that point, it is hard to fault him. While the deco doesn't look like Scourge, it is still striking and well done, as many fans have already said on message boards and social media across the web.
Let us knw what you think of both the reasoning and the toy.