Sure that’s a package manager, but it’s a distro specific one. Now make one that works on all Linux distributions. And now make one that works on all operating systems.
This is the problem that npm, pip, and whatnot solve. They work the same, (almost) everywhere.
Well, the difference between C and Python or Node though is that C is used by the operating system APIs and so it is somewhat tied to each system and their package managers. In contrast, Python/Node exist for the most part at the application layer.
You can install apt / dpkg (or dnf / rpm, pacman, portage, nix, ...) on pretty much any distro. You are really just asking why there's no de-facto standard package manager for C like there is for those other languages.
This is the problem that npm, pip, and whatnot solve. They work the same, (almost) everywhere.
C/C++ don’t have a proper answer for it.