It's possible to create SLO's and check/uncheck the Deployments you want to apply them to on the Service level.
In the case where you have multiple environment running the same (Dive) Service, you may actually have different SLO's.
Specifically, you may have a tiered set of clusters based on SLA's and the budget and SLO's are therefore impossible to configure. By moving the concept of deployment assignment to the objective itself, this would create a huge amount of flexibility that currently doesn't appear to exist.