actually, i was curious about that myself but sort of on both tangents. at the higher end i'm using Unity and PD vanilla via Kalimba and would definitely like to use it without involving too much extra as it is in that situation.
but the embedded factor is pretty important too. i've been checking out Bela which has to compile PD patches using Heavy as well as using Xenomai to make PD work efficiently (and Heavy doesn't support a lot of objects at the moment). i would imagine that Johannes Taelmann was considering something like PD for his Axoloti but couldn't make it work performance wise and so decided to roll his own graphic patching setup instead.
best,
scott