Matt was probably still high being with Katie all last week. You guys have to remember that the morning show grind takes its toll on people and Meredith was one of them. Plus, I think that when she was offered to succeed Katie, it was a once-in-a-lifetime opportunity that she could not pass up at that time. Now that Meredith has done it, I doubt it's something she would want to return to full time. Also, I bet they were going to have Meredith return for Matt's anniversary (which she didn't), and Today's 65th anniversary, so why not have her on for a full week?