Don’t blame Linux as a whole for Thunderbird not packaging a .deb file. (EDIT: or an AppImage file. I get everyone is not on Ubuntu/Debian)
I’ll blame Linux as a whole for every app needing several deb files (one per distro Ubuntu/Debian/etc and one per LTS), several rpm files (one per distro RH/Fedora/etc and one per LTS), and several <100+ chars omitted for brevity).
On other platforms (Windows, macOS, Android, iOS) it’s fairly common to distribute GUI apps as a single binary so you don’t need an army of package maintainers. Perks of having many years of ABI stability.
I can't comment deeply on deb vs rpm, it is kinda disappointing that we have this split, and I don't know if there's a great way to merge it back.
Mac does have a good distribution story. This also exists on Linux in the form of app images. The one missing piece is that Mac has the Applications convention. AppImageLauncher[0] solves this, but really it would be good for Gnome/KDE to just integrate this concept. That gives the (important!) "have the application show up in the application launcher" option.
I do not believe one could qualify Windows programs as being distributed as a single binary. A single installer, perhaps! But many Windows programs dump files all over your file tree to do things, and then goes to touch stuff in your registry. There's a reason we have "portable executables" for windows as its own download option!