SLOs certainly don't rigidly map to OKRs. Maybe it's easier to consider them (two sided) commitments about the quality of service? They're more of an ongoing measure of quality rather than a quarterly objective.
Good point on the quarterly vs continuous measurement. I'm not implying they are rigidly mapped but it makes sense you can put quality changes down as an objective for a team. This can be both end-of-quarter quality but also the general rate of change over the entire quarter.
Depending on the situation, I have seen teams aim to achieve certain SLOs but it can also be that certain other things can be achieved without letting the SLOs suffer (if they're already at a reasonably high quality).
Depending on the situation, I have seen teams aim to achieve certain SLOs but it can also be that certain other things can be achieved without letting the SLOs suffer (if they're already at a reasonably high quality).