Because language bindings isn't really what makes ChatGPT tick.
Sure a project can be based on more than 1 language. But it seems to be mostly python.
https://github.com/openai/gpt-oss/blob/main/pyproject.toml
https://github.com/openai/gpt-oss/blob/main/CMakeLists.txt
Because language bindings isn't really what makes ChatGPT tick.