Curate, connect, and discover
Basically, two elemental masters are not supposed to be together romantically because there is a slight chance that if they have a child, that child wouldn’t inherit one of their parents powers but rather a combination of both of the elements. This could also work if it was two people just related to elemental masters had a child. Like for an example, if Kai or Nya inherited the power of Steam rather then fire or water. I believe that most fusion children would have weaker powers then their parents do but there is always a chance to have a child with great power. Because of the chance of a child having such an overwhelming amount of power this would lead to elemental masters not being allowed to be together and that would provide an answer as to why none of the other elemental masters searched for Maya and Ray after they disappeared. In addition, the chance of a child being a fusion would work on a Punnett square, a one in four chance to be one, to be exact. Also being a fusion would also lead to a new elemental being in the world.
I just really like this headcanon cause it was the idea that most of my OCs stemmed from ngl-