Geographically these make complete sense, but tv market wise ($) it would limit interest too much.
For example, when the Redskins play now there are very interested parties in Dallas, New York, and Philly. Probably add Ravens fans to that who either have a 2nd team, or hate the neighbor team.
When Ravens/Redskins play in your new scenario you actually shrink your interested tv market (by not playing opponents outside the area).