謎底解開:
BA has been eager to re-establish itself in the region and will serve 15 Asia-Pacific destinations this Winter season, including a return to Bangkok and Kuala Lumpur. Interestingly, its Kuala Lumpur daily flight - announced back in March - has similar timings (and the same aircraft, the 787-9) to one of its daily Hong Kong services, suggesting the airline has been planning to drop one of its Hong Kong flights for a while now.
https://simpleflying.com/british-airways-halve-london-hong-kong-flights/