Appimages are not well integrated with Linux desktop environments. It’s also not suitable for installing/uninstalling via command line, which most Linux users prefer to do.
Building a Flatpak package and making it available at Flathub will be ideal, which will allow both command-line and graphical installation, and better integration with Linux Desktop.
Making it available via the package managers (such as apt, pacman etc.) will be even better. But it’s understandable if the developers don’t want to package it for every possible flavors of Linux at the current stage. Flatpak, being distro-agnostic, is a more reasonable choice.