I haven't been the biggest fan of flatpak and generally wish software would either be packaged as an rpm or an AppImage, but the OP makes a pretty strong case for why it's a good idea (because existing options are too niche, and have no ability to incentivize developers who need to get paid for their work. This leads to Linux desktop having far fewer applications available to them compared to windows and mac.)
I do hope the command-line UX around flatpaks (installing, updating, etc) improves a lot though as currently it leaves much to be desired.
AppImage has issues. The guy from Suse who does MicroOS, Richard
Brown, a few years ago was literally walking around giving talk about how bad Flatpak was and how everybody should use AppImage.
In his most recent talk he basically said, he was wrong, the Flatpak people did address most of the issue he had and AppImage was no viable.
AppImage still just works, just like tarball bundles without dependency on 3rd party infrastructure and overengineered solutions like snap and flatpak.
I haven't watched the talk (yet), but I use a number of app images and they have always "just worked" and in remarkable fashion. My only complaint is that you sometimes have to write the .desktop yourself if you want it launchable through the UI, but that's a fairly trivial objection.
Yes definitely, it's probably both. Both are in a feedback cycle as well. Less people means less attention. Less attention means less people. It's a hard cycle to break.
I do hope the command-line UX around flatpaks (installing, updating, etc) improves a lot though as currently it leaves much to be desired.