Why are some package-managers, such as apt and pacman, unable to asynchronously install multiple packages simultaneously, whereas snap is able to?
When I attempt to asynchronously install more than one package via apt, pacman, and dnf, the action is prevented until the previous package has been installed. However, if I attempt what I have previously described via snap or flatpak, simultaneous installation is possible.
On apt, you’ll get a locked only if another process is installing packages. So I suspect that by “install multiple packages”, you mean “asynchronously install packages from multiple sessions”
Snap is a little different in that it effectively installs a container for each application you want to install. That means each container is isolated from each other.
The benefit is that you can install pretty much any version of anything on any version of anything else. The disadvantage is that you install mulitple copies/versions of the same thing.