I once addressed this question about Turkana IV on r/DaystromInstitute:

So do we have a reasonable explanation for why the Federation didn’t intervene in the years leading up to Turkana IV breaking off? The time frame, coincidentally, points us to why the Federation might have been devoting resources elsewhere and therefore didn’t pay attention until it was too late.

The late 2340s saw the start of the Cardassian Wars. Exactly when the Setlik III massacre took place is a matter of debate. Most date it to 2347 because of a line in TNG: “Realm of Fear” (2369) where O’Brien tells Barclay he’s been a transporter operator for 22 years (he was a Tactical Officer during Setlik), but there’s contradictory evidence from other episodes in DS9. We can discuss that another time.

But if Setlik III did take place in 2347, then by that time the Federation was embroiled in a war with Cardassia which lasted, in various iterations, until the early 2360s (POWs were released in 2362, DS9: “Tribunal”).

It might not be a stretch to think that a colony world like Turkana IV slipped under the Federation’s radar until it was too late. I get the impression that most colonies aren’t directly governed by the Federation. They’re given autonomy up to a point, and if they want to break off, then it’s their right to do so.

So criminal gangs or not, there was a war going on and the Federation let it go. Not necessarily its finest hour, but I can see it happening.

Annotations for Star Trek: Section 31 up at: https://startrek.website/post/18738476