It's all a drama ploy. You could say why bother with relationships and just have all the characters engage in open or poly affairs. Because it takes the drama aspect out. Media in general is caught up on the will they or won't they deal.
- So they spend lots of time teasing a relationship & fans tuning in to see if they'll ever get together.
- Then when the characters get together, we'll get the honeymoon period that gives fandom the "awww" feels, followed by the dysfunction where the relationship deteriorates and character brings out the worst in one another. Then fans continue tuning in because the dysfunction is hot or to see if they overcome it.
- Then the characters will break up, and we'll go back to circular will they or won't they. And fans tuning in to see if they ever get back together.
It's just as case of building something just to break it, and start building it again in some different way that'll have the same result.