I think at least part of it is that there are so many solutions for Python packaging, which are often intermixed or only half-supported by developers. It's a tough ask to provide dedicated support for pip, conda, poetry and what else is there plus a couple different ways to create virtual environments. Of course if you do everything right, you set it up once (if even that) and it just keeps working forever, but it is never like that. Someone will use a tool you haven't and it will not work correctly and they will find a workaround and the mess starts.

Also I think that Python packages are sometimes distributed as shared libraries is a problem. When I think about conan or vcpkg (package managers for C and C++), they usually suck because some dependencies are available on some platforms and not on others or even in one version on one platform and in another version on another and you get messes all around if you need to support multiple platforms.

I think generally binary package managers are almost always bad* and source based package managers almost always work well (I think those are essentially easy mode).

*: unless they maintain a source package of their own that they actually support and have a fixed set of well-supported platforms (like system package managers on most Linux distros do).