Using variables in Python files is never counted. This is true for both libraries and Python variable files.
Example: The use of the variable person is not counted because it's used in a Python variable file.
person = "Pekka"
message = "Hello " + person
There is currently no plan to remove this limitation. Reason:
This tool analyzes Robot Framework code. It should not also analyze Python code. There are different tools for that purpose.
If you disagree with this assessment, leave a comment on this issue.