It’s believed that if you do serial fiction, especially fiction that lasts for decades, pairing an iconic character with a love interest is a dramatic dead end. It’s also believed that it ages the characters. People say on shows like Cheers and Moonlighting, once the characters got together, a lot of the tension that made those shows fun was gone (I have no idea, I have watched very little Cheers and no Moonlighting).
I have some sympathy for these concepts, I get why publishers believe them to be true. But so many of my favorite stories had the characters in relationships, I don’t know, I miss them a lot.