Lots of programming languages have their own package manager, separate from the distribution or OS package manager.
Going loosely from the TIOBE index:
- Python has Pip
- C# has NuGet
- Javascript has
npmfor Node.js - Visual Basic also uses NuGet
- R has a repository of packages that can be installed by running
install.packages("something")in R - Rust has Cargo/Crates
- Go has the
go getcommand - Swift has its own package manager
swift package - Ruby has RubyGems
- Java has Maven and Gradle (not sure if they are full package managers, or build automation tools with dependency resolution)
- PHP has Composer for managing libraries and dependencies
- C and C++ are the only exceptions I can think of, off the top of my head; libraries are managed by, and coupled to, the operating system
Simplest answer: it enables programmers on any variation of an OS to get code. If I’ve got a python requirements.txt, getting those requirements installed is the same on any system I’ve got an appropriate python version. The designers of the languages effectively deemed that an important goal and explicitly put in the effort to include package management, in at least most of your listed cases.