Probably because the role actually does still require someone to be able to put out fires while under stress. I've met many otherwise excellent software enginee

Probably because the role actually does still require someone to be able to put out fires while under stress. I've met many otherwise excellent software engineers who cannot or will not deal with high pressure oncall situations. The Operations aspect of DevOps requires a certain level of familiarity and comfort with the type of real-time communication and troubleshooting needed to deal with emergency situations. Some people are excellent with design and implementation work, but do not communicate well enough in high pressure situations to fit a DevOps/SRE role.