I am responding to this old thread because I just made a connection as to one reason my BMW is set to default to comfort mode upon start-up rather than the last setting. It has to do with how the EPA tests fuel economy in cars with multiple driving modes. If the car defaults to a specific mode, fuel economy in tests is based on this mode. If there is no default, the fuel economy may represent an average of different modes. My speculation is that BMW wanted the EPA fuel economy test to reflect that achieved in the comfort mode setting. I am happy the default is not the Eco setting.
https://www.cars.com/articles/2013/0...a-gas-mileage/