It seems like on many shows, family is a bit limited, at least when it comes to regular/main characters. It seems like on most shows that involve a family, or when the family of the main character are major characters, it's often just a household family. Usually just parents and siblings, maybe grandparents (who may or may not live with the main characters). We don't see much in terms of them having aunts, uncles, or cousins, and if we do, we don't see many of those relatives (and if any are major, then we might not see both parents or might not see any grandparents or whatever). Great-grandparents and relatives of parents when the main characters are kids might also be scarce (of course in my life those kinds of relatives have also been scarce).
Part of it could be due to not wanting too many main series regulars on the show, or maybe wanting more than just family in a fairly large cast. But even if the main focus is on a large family, it's limited - The Brady Bunch was mostly limited to just the parents and the six kids, with one cousin being a regular at the very end, and rarely any other relatives get seen or involved. For a smaller family example, there's The Goldberg's, where it's mostly the main family, with both grandfathers being seen a lot (only one showing up regularly while the other shows up from time to time), and one uncle seen on occasion.
I guess Rugrats is one exception to this, as we have Tommy, his parents, both his grandparents (well, both grandpas and his living grandmother), his aunt and uncle, and his cousin. Which seems to be it, outside of distant relatives who don't seem to be there a lot (like Didi's brother and sister-in-law, Aunt Miriam, and the family from Family Reunion).