It would be hard in the presence of parametric polymorphism (multiple functions having the same name but different numbers and types of parameters), as well as the difference between C++'s and Python's method resolution semantics (in Python, for instance, everything is virtual).

Also, templates.

Also, a bunch of other things.

While the mapping between C and LLVM IR is rather straightforward, things are more complex with C++. C++ constructs get dismantled to be compiled to IR, and the binding generator would have to restore all the C++-ish information from metadata and type info, which isn't easy.