on circumstances involving evidence and/or manpower issues with the various agencies involved.

Perhaps some of the original defendants cut deals recently and as a part of those deals they named names which allowed the subsequent arrests.

It does seem unusual that police would expend an inordinate amount of time for simple misdemeanors, but anything is possible.

(still not a police officer)

Statement a few months back that they do not have the resources to investigate and solve all the murders in their district. Now the majority of the murders are gang or drug related so it's just the preadators killing each other and not a real loss to society. The arrests have been curtailed significantly and IMO is that deals are being cut and there was a lot more going on that what was reported.

Many reasons.   I have seen arrests years after an initial raid.  They get records of others that participated but can not find them.  In the Phx Goddess cases, some arrested like 3 years after the raid often in another State.  Only caught when stopped for a traffic violation.  They run ID through NCIC from the machine in the police car and show an arrest warrant.  For those out of state they were held and someone from Phoenix PD picked them up on an extradition warrant.  Even if there was no evidence of having sex at the Temple, anyone employed or associated in any way was charged with felony association with a criminal enterprise.