Systems administration and operations are tightly scoped. DevOps is, in my opinion, an umbrella term representing all non-core engineering work: servers, build pipelines, on-call response, infrastructure, and more.
The tricky part is that a lot of these areas are relatively new, and the older ones like server admin have changed dramatically over the past two decades.
DevOps hasn't failed. DevOps is in its infancy and is going through technical, strategic, and philosophical growing pains.