The problem with AppImage is that it doesn't tackle the core issue of software distribution: how to build the software so that it runs on all the systems you want it to run on.

Flatpak and Snap have SDKs for this purpose, but with AppImage an ISV is forced to guess which libraries need to be bundled and which may be dynamic link dependencies from the OS.

Not to mention the requirement for fuse2, which is being replaced with fuse3.