SRE is the first-responder team. They are on-call 24/7 (the team, not each person), perform systems and service monitoring, triage failures and mitigate outages.
That doesn't mean it's all handwork, I'm sure SREs at Google employ a boatload of automated event handling and custom response scripts. But "keeping the service up" requires different skills than "building a service", and Google chose to separate their Dev and Ops this way. As others said in this thread, if some service isn't up to SRE standards (in terms of monitoring, logging, or robustness), the SRE team won't accept it and Devs would have to do their own Ops.
That doesn't mean it's all handwork, I'm sure SREs at Google employ a boatload of automated event handling and custom response scripts. But "keeping the service up" requires different skills than "building a service", and Google chose to separate their Dev and Ops this way. As others said in this thread, if some service isn't up to SRE standards (in terms of monitoring, logging, or robustness), the SRE team won't accept it and Devs would have to do their own Ops.