@PeteBleackley it's mostly because the moderation is decentralized as well, I think.
Each instance has a small, limited number of moderators that can only handle so much throughput. However, each of those subset of moderators only moderate on their own ruleset.
There are many different rulesets across Fedi that don't always align, so sometimes there are gaps in the system where offending content can be missed for a certain amount of time due to these limitations.
I'm not sure it can be addressed 100% correctly, unfortunately. Simply due to the way the systems work.