One of the main issues still stands. There is no open documentation about how to integrate that into a software, at least I was not able to find one. So even if someone want’s to make a plug-in for Krita to allow using it, they can’t, and the software licenses might be incompatible anyway. I’m pretty sure that Wacom contacted the producers of the other programs themselves and asked them to integrate it or Wacom made the plug-in for them to use.
Krita’s plug-in system would be a way around the software licensing problem but it’s not possible to simply make one, as it seems. Perhaps you can ask them where to find documentation on how to integrate that into other software or how the integration even works if someone wanted to make a plug-in. I wanted to submit a question but they asked for too much personal data in my opinion so I didn’t.