I think the difference is that you can pip install a github url and it will work, it will even work if the upstream has done nothing to package it.
I think the issue could be broadly defined as how difficult it is how difficult it is to take someone else's code and use it as part of your project. For C/C++ the answer can be completely trivial to a massive pain in the ass.
Oh I dunno. With cmake it really is pretty straight forward. You can pull from VCS, a tarball, even use a git submodule.
If it's another Cmake project, that's the happy path. Easy peasy. If it's not you still have the ability to run ./configure && make or evoke whatever incantation is in the dependency's requirements. I'm not the hugest fan of cmake, but I've worked with it quite a bit and it's a much more pleasant story than other languages I've used a lot like python, JavaScript, OCaml (which I love), etc.
I do find rust and go dependency management a little simpler due to the prescribed nature of them, but once you get off the happy path, the flexibility of C land is tough to beat. It sort of matches the language stories themselves; you have more control and have to do a bit more yourself. It's all about trade offs.
I've done it before to integrate rust into polyglot build systems. There's a surprisingly long history of build systems trying and failing to implement rust builds without the "happy path" of simply wrapping cargo. As far as I know no one's ever succeeded.
