I suspect this may be attractive to those based outside London and in Europe, who are BAEC members.
For example, I'm GCH for nearly 3 years now after 2 as SCH. Moved to AMS last year but continued to choose BA where it was within the bounds of reasonableness, requalified as Gold through 2018. Lots of MAN-LHR-AMS runs for personal and 5-6 LH in WTP or J (and 1 GUF to F.) However this year, there's just not enough differentiation to use BA on SH unless the schedule or price makes it the only option. This is new for me, I used to pay more and travel longer to fly BA. Now, I'm just not motivated to and frankly it's more convenient to do RTM or AMS direct for the same price (KL) or half the price (BE.)
Before FB's 'April Fool's Day' debacle, FB was very attractive to me being based near LBA at the time. KL has great regional coverage and personally I find AMS much better for connection (with the exception of BA domestic T5-T5)
I'm now AZ top tier (status match) which is SkyTeam Elite + and have re qualified for mid tier comfortably (still STE+) - I'm considering sticking with ST and letting BA drop to silver. I recently tried both KL and AZ business class and they were pretty good. I was very impressed with Alitalia actually, though that's to be expected as they're loss making. KL was indeed very good though.