The hundreds of billions of people in the Federation who would be helped by the particle were not spying on them. Nor were they the ones who were going to kidnap them. The Halkan's dilithium was somewhat rare, but they were not unique to that world, they did occur elsewhere, the same thing could not be said of the concentrated particles in the ring. In addition, the implication is the Halkan's were indigenous to the world in Mirror Mirror, it was the Halken's territory. It was made clear that the planet in Insurrection was Federation territory (per Picard), and that the Baku migrated there originally (per Anji). The dilithium was their property, a natural resource of their home world. The Halkan leader referred to the crystals as "ours." The particle rings weren't the property of the Baku. The Baku at no point said that the particles were theirs. They did kick the Sona off the planet, and in some way possessed the power to enforce that decision. We saw a single Sona visiting him mother. There no dialog in the movie to indicate that he was welcome to stay, or that other Sona could return to live in the village. The Baku insisting (not simple acquiescing) that the Federation/Sona harvest the ring would have healed the Sona, and extend their lives. As well as doing the same for hundreds of billion of people in the Federation.