Not your parent, but I personally believe that using "package managers" to describe both of these things conflates the issue. That is, both are valuable, for different reasons. The shortest way that I can describe it is this: I use my system package manager to install things for software that I'm not developing, but language-specific managers for software that I am actively developing. When I used to write a lot of Ruby, I had my own install, but now that I mostly write Rust, I have Ruby installed via apt-get.

The two styles of managers just have different goals. That is, a package manager such as apt has the goal of creating a single, harmonious system from stuff written in many languages. But a language-specific package manager like Cargo has the opposite goal: to provide a good way of writing software written in one language across multiple systems. This is where most of the tension comes from. The rest of it is from the same general structure, but with different specifics: the goals of these kinds of systems are very different, and conflicting.

Software is hard.