They shouldn't have made PoE2 a sequel. I couldn't bear to finish the first game and I'm not playing a direct sequel to a game I didn't finish. As for sales, this says it all:
People find PoE boring, so they don't buy PoE2, which looks like more of the same. It's a direct sequel, so newcomers will feel like they need to play the first game beforehand. Assuming they do, they'll most likely find it boring and don't buy the sequel.
People don't find Kingmaker boring, so they buy Wrath of the Righteous. Furthermore, it's not a direct sequel, so everyone can jump in, even if they didn't play Kingmaker.
Obsidian has worse business sense than some ragtag group of Russians, which honestly isn't that surprising considering the gigabrains like Feargus or Parker are still there and still make decisions, even under MS.