I flew as a PM DTW- SLC, and did not get upgraded at all. F went out full. So remember, it is not only rev-management, but also what fare class was bought. If you buy in an upper fare bucket, you'll get upgraded before the LUT fares.

Also, any hub/hub is more difficult, esp if people on the plane have corporate contracts to put them into F, they bought B/Y fare buckets, etc. So there is no "one" reason why you didn't get upgraded.

Dave