Because unlike Linux they don't have to, since MacOS actually defines the concept of a stable base system that can be targeted by applications. Docker exists in part because the Linux world has no such concept.
Thats the point here. The two aren't similar at all.
MacOS apps contain all the app. Mac Apps leverage all of the OS functionality they can. They are strongly tied to MacOS and rely on it for most functionality. When I upgraded to Big Sur, the Mac Apps that run on my computer adapt to the changed OS libraries and often present differently.
Docker apps contain their own complete environment. They are deliberately engineered to disassociate from the base OS.
Electron is a sort of middle ground largely ignoring many system libraries, but using others.
The only thing Docker has in Common with Mac Apps is the fact that they keep associated files bundled together.
