Personally I believe this is a direct result of the absolutely massive devaluation of the term "DevOps".
The latter has become a synonym for meaningless mishmash of "everything in operations, and nothing in particular". Using the term SRE is a clear signal that we're talking about engineers with good understanding of systems and operations.
Disclaimer: this distinction is mine, and I have come to it after making the mistake of trying to hire "devops engineers". Put those two words together and your applications pipeline gets crammed with unskilled remote hands who cannot even realise they have delusions of grandeur. It's also - apparently - an invitation for every cold-emailing recruiter to spam you to death.
If you're looking for members of that school of thought, you say SRE. If you're comfortable having a "boiler room" and just need to staff it up, the terms sysadmin and devops work just fine depending on the level of coding involved.
Many more people are paging operators to do DB replica promotions by hand, than are inplementing distributed consensus algorithms and self-healing distributed databases.