I wonder if it's because of the context of the comments
FB says hate speech is "We define hate speech as a direct attack against people — rather than concepts or institutions— on the basis of what we call protected characteristics: race, ethnicity, national origin, disability, religious affiliation, caste, sexual orientation, sex, gender identity and serious disease. We define attacks as violent or dehumanizing speech, harmful stereotypes, statements of inferiority, expressions of contempt, disgust or dismissal, cursing and calls for exclusion or segregation. We also prohibit the use of harmful stereotypes, which we define as dehumanizing comparisons that have historically been used to attack, intimidate, or exclude specific groups, and that are often linked with offline violence. We consider age a protected characteristic when referenced along with another protected characteristic. We also protect refugees, migrants, immigrants and asylum seekers from the most severe attacks, though we do allow commentary and criticism of immigration policies. Similarly, we provide some protections for characteristics like occupation, when they’re referenced along with a protected characteristic."
Maybe in whomever is reading it when it gets reported doesn't meet the definition of hate speech. I can absolutely see how using the term can be against their standards so either it's always being overlooked or there's something in the way the comments are phrased and used that means they are awful but aren't actually against their standards. But I also think FB has a long way to go and they try to tread too carefully sometimes in not taking action.
