I believe nobody says that. But when promoting a "full-featured" 3D animation software like C4D one needs to make sure most part (and most "creative" part) is accomplished using the promoted software. C4D isn't advertised as a hub but rather a content creator. Yes you can do compositing is AE or NUKE or Fusion but major assets (and their processing) should come from your own DCC.
If you are promoting A MAJOR C4D RELEASE then ask yourself:
Does C4D do sculpting? If yes, then Avoid using ZBrush... show what C4D can do
Does it do rendering? If yes, then avoid using Arnold (You'll use Arnold if you are promoting it's new porting)
Does it do character animation? If yes, then don't use Maya
Does it do compositing (at its core)? If no, then use AE, NUKE, FUSION etc.
But if you are doing a NIKE commercial, then you can use anything. Luckily MAXON doesn't do commercials.
So it's ok to use Maya to create crazy character animation to promote Cinema 4D?