SLAs aren't about guaranteeing uptime. They're about setting consequences for downtime.
But once there are strong consequences for downtime the service provider is going to set up training, monitoring, oncall, etc to make sure things stay within the SLA limits. So you are effectively negotiating uptime.
The only SLAs that matter are the ones where service provider will suffer serious $ penalties on braking the SLA. Which rules out basically all major cloud providers that will simply issue credit for the downtime.