That’s the thing too: IMO, one of the things that makes a successful family is a significant presence on the canvas as a unit. Some of these writers can’t think past their short-term story needs, grafting these randoms on to some family in order to gain audience acceptance, but not really thinking past that. These characters sometimes don’t even meet their siblings and other relatives, as those links don’t matter to the one-dimensional stories the writers want to tell.
Family links have become devices for writers to play with in their stories, as opposed to real foundational connections that allows them to explore their characters and their psychology. I’m sure that’s one of the reasons why networks don’t want these characters to be too specific. They can’t suddenly do a “Surprise: Jeremy Stark is Sally Spectra’s dad” story on Y&R if we know too much about Sally.
Then you have all of these weird retconned switched-at-birth stories that impact long-running characters. (Like Jill became a Fenmore on Y&R for what purpose even?)