Rusthon has special syntax for directly using PyObject's from the CPython CAPI. The -> operator is used on PyObject's, and is transpiled into: PyObject_GetAttrString(ob,name), for more info see this wiki page. This allows you to directly manage calling CPython functions, cast and move data back and forth from C++ to the CPython interpreter. This makes using complex libraries simple and safer, you do not need to depend on complex wrapper generators, or depend on C++ reflection to dynamically bind CPython to C++.
Unreal has a C++ reflection system, and this can be used to generate bindings to a scripting language. Unreal users want scripting support, see this thread, and this one asking about CPython in Unreal.
Scripting is great when you have a command-prompt and can type code at runtime, or write quick scripts and simply run them. Scripting fails when you need to do something complex and use multiple threads, for this you need C++. Rusthon allows you to write in a Python-like language and create fast glue code that bridges CPython together with any other C++ library, no reflection or generated bindings required.
This example: unreal_cpython.md shows you how to connect CPython2.7 with Unreal. The example contains no handwritten C++, instead the code is transpiled to C++ at compile time. The embedded Python script is also inlined into the final binary.