There's only one of a several conclusions are maybe all of the above.
1. Either they were incompetent and did not heed the warnings included in the embassy reports.
2. No one with any authority read the reports so they were grossly negligent.
3. They discounted the reports as a matter of political strategy and intentionally tried to cover up their collusion.
They will of course say that they were sharing information as the intelligence/investigation clarified the situation but if that was truly the case then the timeline makes it clear that the left hand didn't know what the other left hand was saying/doing.