Because people love watching Rutgers and Maryland play?
The subscription model of the Big 10 network is the reason why they're valued assets--they added new states and media markets. The populations, regardless whether they watch or not, are stuck paying for that content, so Big 10 wins.
This is why ISU won't get into the Big 10, regardless of their AAU status, perfect geographical fit, perfect cultural fit, etc, since Iowa already has the Big 10 network and ISU won't add anything there.