BA has an incredibly poor track record in letting customers know about operational changes. A few times this year alone I ended up on a different CW seat (obvs much worse than the one carefully selected in advance) and nobody bothered telling me in advance so I could try and sort out a mitigation plan.
I do understand the OP frustration. I guess one flies F also for the privacy and secluded atmosphere of the cabin. Having to mix and mingle in a larger environment could be a just cause for swapping flights - if one is told, of course.