No it doesn't make sense. They can cancel the flight for any reason they like 14 days ahead of departure, so commerciality is a red herring, but it remains their responsibility to ensure you were told about it, whereas I recall you said were only told about this on the day of departure. Original post here, so that people can keep track.

So you have little choice but to give them 16 days notice that you will invoke MCOL unless they can provide proof under Article 5.4. I hope you kept screen shots of what BA.com or the App showed at the time, that would be enormously helpful at this point (they may still be visible in the App if you used this).