It's difficult to say this, since Facebook's report system is semi-automated. And with the amount of Facebook flags the human moderators get on a daily basis, it's just so easy to pass and misjudge a post.

Unlike here on Hive where we are all working with mutual benefit towards strengthening the network, FB is corporate after all. People are paid to moderate, and sometimes considering 15,000 content moderators vs. 2 Billion users, it's quite difficult to assess the quality of these moderations. Some of them may be subjective, others might just be approving whatever report comes their way for the sake of clocking in for work.