The max 7 is the same size as the 737-700 is the same size as the A220-500. With all the training and parts etc set up for the 737 max not to mention the orders why get a new airframe that's basically what you already have?
maybe they're looking at the A220 because they want a bigger Boeing and Boeing knows that whatever they buy next they'll order at least 200 of them and its posturing.
regardless it's always posturing and trying to get a better deal.