Cases like this might have made me think that some loyal frequent flyers have just what they stuck to because of habit.

BA's changes to BAEC might be the breaking of the surface tension that gets people to change their habits dramatically - in the case you've quoted, a bigger propensity to try SQ or another non-OW product with First on it with its ancillary benefits.

There's an interesting MyLondon article about how a number of people who were forced to use the Elizabeth line in 2022 during a tube strike did not go back to their usual commute patterns after the strike, which also cited a 2015 seminar paper by researchers at Oxford and Cambridge (that was later published in 2017 in the Quarterly Journal of Economics - which is one of the highest-ranked economics academic journals around). Essentially, consumers will find better-off solutions when provided with an external encouragement to try (in this instance, the change of BAEC's tier point accural system). BA might not like the results of this experiment when oblivious people start to realise their product offering is highly unsatisfactory in today's competitive market.