As Hoch has said I think carry on is the main driver. On business timed flights luggage space in CE can be a joke especially row 1 or 2. I have often noticed those that are hanging around the gate area ready to pounce as soon as boarding is announced have the max amount of luggage.
Now if BA could speed up luggage delivery maybe less people would carry so much.
Oh and yes why not call F and Gold then J and Silver before others. Also limit young children to under 5s maybe and one parent per child....