Honestly I think that Aeromexico has had a shift in its program. I did enough travel that in previous years, I would have easily qualified for Platinum, and checking my status for next year, I am well short of the mark. In the end, since it really doesn't affect my travel, I didn't check it too closely.
It seems like AM is basing miles of Spend more than distance, as a number of identical trips in identical class are all earning different miles...