I mean
[SPOILER/SPECULATION]
despite doing what they had done, Gulool Ja, bastard son of Zoraal Ja, is technically still the heir and Wuk and Koana are still his family. Come to think of it, he would also have a claim to the throne of Tural. Though he is still too young to make important decisions so whatshisface is likely doing that for him, making him the current regent.
Since for the sake of diplomacy and because Sphene was, despite everything, beloved by the people, the first act was to hold a funeral for Sphene. Because it was an effort to better relations and because Sphene and Zoraal Ja forced their hand.
Alas, someone, either Evil/Imposter!Sphene tampered with the regulators or the regent himself, in an effort to get rid of the heir, and resume the plan.
Coming back to DM NPCs, some people also seem to struggle with NPCs lying straight to their face.
In short:
Like in Heavensward not everything is Sunshine and Rainbows immediately after the Big Bad(s) is (are) deafeated.
[EDIT]
Sorry for the word salad and the typos.