Why does the WWE hate happy couples?

Serious question - every single happy couple in the WWE are heels. The Miz and Maryse, Lana and Rusev, Mike and Maria Kanellis, Stephanie McMahon and HHH... the list goes on. If a babyface is in a relationship with another WWE superstar, such as Dean Ambrose and Renee, they keep it off the camera.

To be clear, this strange rule doesn't offend me, but ever since noticing it, it has me puzzled. Is this some kind of lazy trope, similar to the heel foreigner vs. the face white USA guy? Is it some kind of way to connect with their assumed audience, disaffected "lone wolves" who distrust anyone in a happy relationship? I would love to hear what people think, because as much as I enjoy wrestling, I don't really understand this aspect of the storytelling.