1. It makes organizations slow and inflexible. I used to joke that as soon as another team was involved in something you needed to do it would probably take a quarter. why? Well what you wanted probably wasn't on this quarter's OKRs so it would be an uphill battle to get them to do it. You'd have to argue about getting it into next quarter's OKRs;
2. OKRs can be structured in such a way that you can grade quite well while having achieved absolutely nothing;
3. Teams can be held to different standards. Some get easy OKRs. Some get harder OKRs. So it's still subject to the political-perception problems inherent in such organizations;
5. It is largely for show for upper management. I've been in 2 hour planning meetings where a bunch of teams speak for 2 minutes about what they're working on. This might be useful for directors+ but is really a waste of the time of 50-100 other people. This is a problem with status meetings too;
6. Even grading OKRs can be subjective and political. I recall one famous example where someone (cough Vic cough) said they had a goal of 100M users. They actually only got to 10M. Grade? 0.7.
There was a running meme at Google about feedback that went something like this: This project would've failed without this person. It failed anyway but it definitely would've without this person.
I like this meme because it illustrates how the same set of facts can be used to argue how someone did a good job or a bad job and the difference between the two is whether or not the org likes them. The same set of facts can be summarized as "this probject failed to ship" and "we failed fast, learned a lot and will take those learnings into future projects".
OKRs suffer from exactly those same problems.