BECAUSE WE PRACTICE:
Because we practice the proper way to handle a loss of cabin pressure, and we have to show examiners in the simulator, over and over, for years, we would LIKELY do it the right way in an emergency because it is now the easiest way to deal with things.
THE WEAK point is that the oxygen system is not duplicated at the source of the oxygen. We have two engines on the plane, but only ONE cylinder of oxygen. (cockpit).
IF the oxygen masks dropped in the main cabin, flight attendants with "WALK AROUND BOTTLES" would eventually check on the pilots if possible. PA announcements from the cockpit would preclude the need to check on them.
IT IS Likely the passenger oxygen system was a design with oxygen generators, BUT SINCE I AM NOT a pilot for GERMANWINGS, I ask this question:
IS THE MAIN CABIN/PASSENGER oxygen system a cylinder or individual oxygen generators?
I hope this is a reasonable question and not flamed like what happened to old boeing driver's reasonable question.