This would be foolish marketing. A predictable recurring bonus is no longer a promotion, it becomes the de facto normal transfer rate. BA is willing to sell some Avois to American Express Canada at a discount, but when this type of offer becomes predictable the discounted proportion grows, and the transfer bonus shrinks from 50% to ~20%, as we have seen at American Express (USA) and Diners Club (Canada and USA).
Though in a marketing standpoint it is very foolish, the market share for BA in Canada is quite small compared to Aeroplan. As well RBC has been doing 50% bonuses to BA every year at the same time, often bi-annually for several years now. RBC is very predictable as to when the transfer bonuses will occur, RBC remains profitable and so does BA. Furthermore the RBC Avion product is much more widely used than the AMEX cards anyway, especially in Canada where VISA and MC dominate the market share. It only makes sense from a marketing standpoint that AMEX increase its cardholders.