Oxygen masks definitely aren't unimpeachable good. Passenger oxygen mask systems are virtually never needed but have caused multiple fires that destroyed planes and killed people. They are an expensive complication without which plane travel would be better - the plane would be cheaper to build, there'd be more room and weight available for passengers or luggage, and we'd all save time on safety briefings from not having to hear instructions on how to do a thing that you certainly won't need to do.

The pilots need oxygen masks as a backup while they quickly descend to a safer altitude. Unless you're flying over the Himalayas and can't drop that low, the passengers should be fine.

https://en.wikipedia.org/wiki/Emergency_oxygen_system#Incide...