The genasi of the Maelstrom have done so much to protect and serve Orin’s grandfather, the King. Orin has nothing but good memories of his people, and the whole purpose of his adventuring is to become a stronger man, in anticipation of his future responsibilities. He may never be a king, but he’ll definitely be called upon to protect his family’s kingdom, to the death if necessary.
Orin grew up hearing how his grandfather’s efforts to ally with Neverwinter’s nobility failed, all because of the nobility’s fear, distrust, and general lack of concern for the Maelstrom’s tiny, isolated population. That nobility fell in the Cataclysm, and it’s unlikely that their descendants share the same prejudices that their ancestors did, but Orin would rather put new blood on the throne than see the children of Neverwinter reclaim the crown.
The swordmage sides with Lord Neverember and his forces. They are outsiders who are already well established elsewhere in Faerun, and they have none of the old prejudices and bad blood in their history that Neverwinter’s family does. What’s more, Neverember is cleaning up the city, bit by bit. If he can do that for Neverwinter, why can’t he bootstrap a small nation like the Maelstrom and give his people the glorious kingdom they deserve? Maybe if Orin proves himself worthy, he can earn Neverember’s favor and secure his people’s future.