Animated Optimus is kind of a hard figure to redeco:
*Ultra Magnus looks nothing like Optimus in Animated, so that deco is kind of a non-starter.
*Nemesis Prime and/or Scourge, while technically possible, is there really any demand for a not-quite-Animated version?
*Shattered Glass might have some fans...
*Toxitron would be a straight redeco, but we just got a whole Toxitron capsule line, so they might want to shy away from that
So that just leaves:
*The Motor Master: Existing character, remold the head, still an 'evil' Prime redeco, but also fairly eye-catching. Probably the best option they had, reasonably faithful to the Botcon figure, though certainly not everyone's cuppa tea.
*A new, previously unused deco. I would like to see a Prime in green with silver accents, or yellow with gray. Or, there's Powered Convoy blue. Problem is, outside of the rock dudes, it seems like we aren't getting much in the way of new characters, and the redecos tend toward the 'safe' or 'expected' end of the spectrum.
In the end, I think The Motor Master was probably the best choice of the existing redeco characters they had. I'm not sure I like it enough to get one, but if every Transformer offering catered to me, it would be called Gobots Legacy...