Sigh … lets be clear here. Tyrande treating the Nightborne with contempt and mistrust was both totally in character for her, and justified from her perspective. And since she is both the sole political and religious authority of her people, and not even the most extreme High Profile rep, her word and opinion carries a LOT of weight. Thus, when you consider the “stipulations” of the Shen’drelar being allowed back into the Kaldorei, it makes sense that the NEs would be extremely hesitant to reconnect with a group of Highborne relics with enough strength left that they can’t just bully and “humble” into cultural restrictions and suppression. And yes, that is what they did to the Shen’drelar, as even Malf (a progressive by NE standards) required them to be utterly broken and desperate to let them back in … while deeply restricted.
However, none of this justified resentment and suspicion for the NEs means the NBs have to put up with it. The NEs holding nothing but contempt for what the NBs represent makes sense, but the NBs don’t need to bow before them. And if you play BOTH sides of the Surumar Campaign, it is very clear that Tyrande is not there to save the Nightborne. She is there to fight the Legion, and the Nightborne are bodies she intended to use to spare NE lives in that conflict. And despite Liadrin’s “Playing Politics” in the recruitment scenario, her reasons to be in Surumar are a lot more personal … with the well being of the Shal’dorei in mind. Since she knows better than anyone the horrors of extreme mana-withdrawel and what it feels like to have a beloved leader betray your people to the Fel. Rommath is just there to talk Arcane Shop and Geek out.
So … long story short. It makes sense for the NEs to not want to open relations with the NBs. It makes sense for the BEs to want to open them. It thus makes sense for the NBs to be open to building relations with the cousins that want relations with them (and share many interests), over the siblings who hate them for their culture … and don’t. Frankly, if the NBs had joined under Jin instead of Sylvanas … I don’t think there is a single legitimate argument you could have made against that choice. But … like all of BfA … its who they joined under and when they joined thats the problem. To the point where they themselves regret doing so during the expac, and akin the Horde to the Legion… God I truly hate BfA…