I think the problem lies in compatibility with other DAWs.
So many people using other DAWs wanted to buy it,but couldnt since its tailored for Cubase.
Some people say they are toys.Well,certainly very handy toys.
I use the PD mostly for key commands as it reacts better and faster than a keyboard,its also a time saver for testing drum kits etc.QC,AI and CH are also very handy.
I would say these are very good controllers and im sure the only problem they`ve had was with the lack of integration with other DAWs.