It's more than US World and News Reports ranking. One of the P5, the Big 10/11, requires all members to be part of the CIC, a research consortium. You may have noticed that UConn is spending more money on research these days. I don't know if UConn has applied to the CIC for membership but as of today, it is not part of the CIC. This pretty much eliminates the Big 10 as a possibility at this point in time.
While academics have always played an integral role in the conference, presidents of the Big Ten member institutions formalized the primacy of academics with the establishment of the Committee on Institutional Cooperation (CIC) in 1958. The CIC was formed as an academic consortium of all Big Ten universities and founding conference member Chicago. In 2013, the 15 schools currently constituting the CIC produced over $10 billion in funded research, $4 billion more than any other conference.
Source
From the About
CIC web page:
Headquartered in the Midwest, the Committee on Institutional Cooperation (CIC) is a consortium of the Big Ten member universities plus the University of Chicago. For more than half a century, these world-class research institutions have advanced their academic missions, generated unique opportunities for students and faculty, and served the common good by sharing expertise, leveraging campus resources, and collaborating on innovative programs. Governed and funded by the Provosts of the member universities, CIC mandates are coordinated by a staff from its Champaign, Illinois headquarters.
CIC Member Universities:
University of Chicago
University of Illinois
Indiana University
University of Iowa
University of Maryland
University of Michigan
Michigan State University
University of Minnesota
University of Nebraska-Lincoln
Northwestern University
Ohio State University
Pennsylvania State University
Purdue University
Rutgers University
University of Wisconsin-Madison