There a few different ways to slice your question, but one thing to consider is that there are very different "types" of intelligence "agencies/units".
If we use the broad definition of intelligence which might be something like "gathering and analyzing information to provide guidance to decision makers", and then label any group capable of information gathering and/or analysis as an "intelligence agency/unit", then you can see why they'd appear to proliferate everywhere.
Everyone with executive agency wants their own analysis capability. And everyone with executive agency probably wants their own gathering capabilities as well. And all for pretty reasonable seeming reasons. Technical specialization, time/latency/bandwidth considerations, risk tolerance. There are lots of reasonable reasons why specialization and localization makes sense.
Now the challenge obviously is to make sure you balance that against waste in resources, stuff getting lost in the shuffle, and straight up political infighting.
If we use the broad definition of intelligence which might be something like "gathering and analyzing information to provide guidance to decision makers", and then label any group capable of information gathering and/or analysis as an "intelligence agency/unit", then you can see why they'd appear to proliferate everywhere.
Everyone with executive agency wants their own analysis capability. And everyone with executive agency probably wants their own gathering capabilities as well. And all for pretty reasonable seeming reasons. Technical specialization, time/latency/bandwidth considerations, risk tolerance. There are lots of reasonable reasons why specialization and localization makes sense.
Now the challenge obviously is to make sure you balance that against waste in resources, stuff getting lost in the shuffle, and straight up political infighting.