This.Romantic relationships among characters of different franchises usually don't go well, all is needed is the writer or editorial of one those franchises wanting it to end for things go off the rails. Also, usually the character of the less popular franchise end up getting craped on as a result of the break up.
But even when things aren't that bad, the truth is that it will never be as iconic as Superman and Lois, Spider-Man and MJ, Reed and Sue, Batman and Catwoman, Cyclops and Jean, Cyclops and Emma and now Aquaman and Mera. The lack of stability, the fact that both characters come from the different franchises that sometimes are runned by people with different interests will always get on the way.
Let's look at Storm and T'Challa. When they first got together, Hudlin wanted her, and he had enough pull to have her and T'Challa as a couple, or maybe no one on the X-Men side wanted her enough to fight to keep her under the x-office control. As a result of it, she was basically left out of any major role on the x-books during at time when great changes happened to the franchise as a whole, changes that catapulted character into a popularity that they didn't had before, like Cyclops and Emma Frost.
Now looking at things from Black Panther perspective, the character and Wakanda are having a large portion of it's mythos tied to a character from a different franchise, that can at any moment be taken away by a different editorial office. Let's say that Coates decides to end his run turning Storm into the new patron godess of Wakanda and having her be the new person in charge of Wakanda mystic defenses. Then 2 months later Hickman decides that Storm was never an actual godess, that she and Cyclops are in love and have them move to Mars to establish a base from Krakoa there. That would make a major part of a 4 years Black Panther run not just invalid, because a lot of pages that should be used to promote a in house love interest to the main hero was wasted on a futureless relationship with a character that the BP editorial have almost zero control over.
Give Storm a love interest from the X-Men books.
Give T'Challa a love interest from his own books.