I was remarking on it being required, not if it was available. Typical hypoxia causes** lead to the victims having no idea of the seriousness of the problem, so they would never start an emergency response. They should already have oxygen available - they just don't choose to use it.
**In the non-aviation cases it occurs when some volume is filled with atmosphere displacing gases. One horror story was a rail road tank car that a guy was sent to clean out. His buddy noticed he had taken too long and went to the car, climbed up and, looking down the hatch, saw the guy motionless at the bottom. So his buddy climbed in to help, and also died. They get confused, often giddy, and then die. A second pilot might not help.