For flatpaks and snaps, there is a centralised repository, and hence there is an easy way to update them from the terminal using a single command. I am yet to find such a thing for AppImages. What prevents us from building a curated list of AppImages from which they can be downloaded and updated?
We don’t want it. We want to get software directly from the download pages of the original software authors. Nothing centralized. No terminal needed.
Just go to the download page of the application author and download directly using the web browser, like we have been able to do on Windows or the Mac for decades.
That being said, nothing stops app stores and software centers from distributing AppImages if they like. itch.io, openDesktop, Nitrux and some others actually do.