The Fare Class option disappears when you check the "Book Sky Miles Award Ticket" box towards the top.
So if you search for non awards ticket, the choices returned (which are different than the awards ticket options for the same dates, same routes) aren't necessarily going to be available as awards are they?
For instance, if I search for SFO-CDG awards, the AF nonstops do not shop up at all but if I search without that book awards box ticked, you see the AF flights.