https://github.com/python-poetry/poetry/issues/1122 is probably the issue mentioned above.
Also, from requirements.txt:
# Backward compatibility
enum34; python_version < '3.5'
That line has been there since 2017
All the requirements.txt are popped in the call to setup(), for both the setup_requires and install_requires keys. So all I can see that could be an issue is each of these have a newline at the end, and there are comments as well (though, they are supposed to be handled without problems by pip). We can easily strip them out, and see. But I see the correct stuff coming back from pip (commented in that ticket on poetry).