I'm sure it's a combination of factors of why it's suspended long term.
On the BA board, they are reporting that BRU is reopening next week but only with 20% capacity - and they don't know how long it will be before capacity will be increased. So all airlines having to make cuts, no matter loads, projected revenue, etc. I suspect that the airlines may have been told that the 20% capacity is not just flights, but total passengers as it seems the limiting factor is not gates but rather check in space and security, so changing to a larger plane may not have been possible.