I think it has to be a personal pissing contest between the CEOs of Marriott and American Airlines. Kind of like when Blue Cross/Blue Shield and Baptist Hospitals stopped working with each other about 15 years ago. Why would the biggest health insurer and one of the biggest hospital systems stop working with each other to the detriment of patients? Because almost assuredly, two male executives at the top of each company made it personal and wanted to prove their member was bigger than the other executive's member, beat their chests, took their balls and went home.

It makes perfect sense, and really is the only explanation in my mind that does make sense.