Thanks for the thoughts, but actually the plane is almost EMPTY! I don't have a n availability tool, but it seems highly unlikely that there are not ANY reduced rate seats available (six weeks out). So I still don't get it. I suppose it could be an error.

I guess I will have to call them and ask if I can reroute without a change fee before my ticket is irrevocable. And see what they tell me if they claim only FC fares are available when the seat map shows the back is wide open.

That will help to determine whether it is indeed chicanery or "honest" marketing strategy!