Because a package manager for C++ is infinitely more complex than one for a bytecode language like Java or .NET, where theres either a well defined spec (.NET) or a reference implementation (Java, Python) that everyone measures compatibility for?
The first obvious problem is that there is no ABI for the C++ standard library. This makes sharing any kind of binaries plain impossible because exchange of C++ standard library objects between your project and a binary from the package manager will very likely just blow up. So the package manager, right from the bat, has to build every library and every (recursive) dependency of that library on demand on your computer using your C++ development environment. That alone is a herculean task if you consider the number of compilers (GCC (MinGW), Clang, VC, ICC), their respective versions and possible C++ standard library implementations used. And remember: you can't mix and match!
There is a reason even a C++ library such as ZMQ exposes only a C interface, and it's because things become extremely messy very quickly when you are juggling around native code.
The first obvious problem is that there is no ABI for the C++ standard library. This makes sharing any kind of binaries plain impossible because exchange of C++ standard library objects between your project and a binary from the package manager will very likely just blow up. So the package manager, right from the bat, has to build every library and every (recursive) dependency of that library on demand on your computer using your C++ development environment. That alone is a herculean task if you consider the number of compilers (GCC (MinGW), Clang, VC, ICC), their respective versions and possible C++ standard library implementations used. And remember: you can't mix and match!
There is a reason even a C++ library such as ZMQ exposes only a C interface, and it's because things become extremely messy very quickly when you are juggling around native code.