Losses matter.
Michigan with 5 including one out of conference (and Washington)
Iowa with 5 including 2 out of conference (and Michigan state)
Minnesota with 5 including 1 out of conference (and Rutgers)
Rutgers with 6 including 1 out of conference (and UCLA)
USC with 6 including 1 out of conference (and Maryland)
The next best options to be ranked for the big ten all had too many losses. And not just at the hands of good teams.
The big ten probably has 7 teams between 20-50 though. Those 5 plus Nebraska and Washington.
If Michigan beats Washington, Iowa beats Michigan state or Missouri, Minnesota beats North Carolina, Rutgers beats UCLA, and USC beats Maryland…they might all be in the top 25