Not saying lock-out should be ignored, just that sometimes the task can't be completed without the device being energized, and a safety function disabled or a person at risk.
At least one of those guys screwed up (the one killed), maybe both.
When I worked with robots only a couple of us were ever allowed in the cages (We called them caves) when they were operational. There was plenty of room to move around them but you had to be aware of where they were in their work cycle.
They mostly moved in a small area swinging slowly from left to right as they worked because they painted parts on a line. The right to left swing back to start the next set of parts was where the real danger was because it was a fast sweeping motion.