Regarding BRU, I think BM must be confident with it to be going 3 daily, they probably get quite a lot of last minute bookings paying the higher last minute fares, probably in their equivalent "business class" too. Just making an educated guess based on BRU's clientele, one lives across the road.
And regarding EK selling F, do they need more crew? I thought it kind of boiled down to "an amount" crew for "an amount" of seats, whether they are filled or not. But I suppose it's for the levels of service in First