Why does Adobe Reader require an installer? Does anyone know why Adobe Reader requires a permissioned installer application, rather that simply existing as a self contained macOS application bundle?

What system level configurations is the installer making changes to, and why does Adobe feel they are needed for a simple PDF reader?
The Acrobat Reader installer not only installs the application itself into /Applications but contains a bunch of other packages which need to get installed into other places (e.g. browser plugins). These things can't get installed by just using a simple application bundle (at least not as easily).