I have the same situ, my company tkts are booked by a TA and cannot be upgraded online. Earlier this week, I did the LHR - Cape Town flight and wanted to upgrade to CW because I needed a bed for the sleep having had a mtg brought fwd not allowing me to R&R for half a day on landing.
They only offered me WT to WT+ for £209 and couldn't sell me an upgrade to CW, even though I said the price was immaterial (within reason) so I went for the WT+ as I was told nothing else was released.
I counted 6 empty CW places on the flight.

I don't get it, but that's how it appears to be.