Both Apt and DNF/Yum, the two most popular package management schemes for Linux distributions to my knowledge, only support system-wide installation of packages: Files owned by root, binaries go in
(/usr)?/s?bin, settings go in
/etc and so on.
Now, on systems in which there are multiple individual users who don't have root privileges, it very often - if not always - happens that a user wants to install some apps or utilities which are available for that distribution; and s/he is fine with an installation that's personal and not common to many/all users.
Now, it does not seem a far-fetched or even incredibly complicated idea for packages to be adaptable, at installation time, with a different root directory or set of root directories, so that users can do this. Nor is it much of an issue to manage a user-specific registry of installed packages (whether or not an individual user has his/her own package DB).
So what's the reason that this functionality has not been added to those common package management systems/schemes?
Note: This is an informative question, i.e. I'm asking about what people know about the past, not what people think about this feature.