Google's SRE was always about building infrastructure to make things reliable, and started in a world where LAMP on bare-metal + DNS load balancing was common. It makes sense to have a separate org/team/role responsible building real load balancing with health checks and failover, figuring out how to do zero-downtime updates, etc.
When these problems because largely solved with off-the-shelf software SRE became either a bureaucracy (ensuring reliability through policy and enforcement) or just deploying other people's code and holding the pager.
When these problems because largely solved with off-the-shelf software SRE became either a bureaucracy (ensuring reliability through policy and enforcement) or just deploying other people's code and holding the pager.