“Though Judah became prominent among his brothers, so that a prince was from him, yet the birthright belonged to Joseph.”
This biblical author justified a prince from Judah and its prominence without indicating why that should be. Nothing in the relationships with the 12 sons of Israel indicates that Judah should be first. It just happened, de facto, without a rational. There seemed to be a conflict between the people of Judah and the sons of Joseph from Ephraim and Manasseh. The biblical authors clearly favored Judah.