It may apply only to the nonstops MIA-BNA, but I'm not certain (the aa.com fare rules don't say and I didn't look at Expedia for permissible routings). From the sale hyperlink, I entered May 12 to May 20 and got $156.90 all in when I selected the nonstops, but much higher fares when choosing the connections. The nonstops are Q, while the connections involve L and other fares. Alternatively, perhaps all the sale seats are taken on the dates you want to fly.