Many like myself don't like the old idea of downloading stuff that "just runs". It's too much going back to the old ways with windows where you randomly just downloaded a binary off a website and ran it.
Basically it's the equivalent of sideloading apps on mobile devices. I won't do that either unless it is required.
Now I do have one such app, in appimage which is my preference anyway. KDEnlive, which I run as an appimage Vs the Debian package only because I'm on Debian 10 on my main machine and have yet to pencil in the upgrade time.
Now, GNU Guix is interesting. Cryptographically secure and verified compilation (or pre-compilation) of source code straight from GitHub etc. Now, that will be more like it!
Appimage IS an attempt to bring windows style software (mis)management to windows. Flatpak is more like bringing android style app management along with limited permission sets, permission portals, and some sandboxing. It also leverages the server spaces container principals more and more to do!
Guix is also super cool! In fact using guix to build OCI containers and flatpaks to me is natural evolution of the declarative/reproduce able image concepts introduced by both.