The issue here is that such group is still way too small. But sure, I may be wrong too, it happends every now and then 
But out there isn’t that many forums where userbase is that massive there users would be willing to pay anyway. People just don’t want to buy an app to get support.
And I’m quite sure if there would be a real opportunity to make revenue someone would builded a native Discourse-app already.
For me as a microlevel forum admin I would like to see such app. On my area PWA is just too difficult start to use for ordinary phone users, and DiscourseHub is even more harder — for reasons I don’t totally understand, but mainly because it is in English I guess. Most of finnish can enough English, but still the barrier is way too high — yet they can use other English speaking apps without any troubles. But I claim that this is question in Spanish/Portugese world, Italy, France, even in German speaking Europe.