Someone isn’t reading much science fiction - there’s plenty of families in them, but they aren’t always seen because the point of the story is that it’s full of adventure and daring and exploration and research and death and so on. Not something most people bring their kids along for. Also, many times the leads are single specifically to allow the reader to insert themselves into the story no matter their background, anyone can relate and remember when they were single and free to be able to do something like a sci-fi adventure! A few off the top of my head:
Ender’s Game - kid is taken from his family because he’s crazy smart and develops a new family with his fellow squadmates.
The War Against the Rull - the main guy has a family back home, that we see occasionally. And, he basically adopts the alien baby in the process.
Star Wars - per the article, Disney’s stupid crap is different, but the real storyline includes Han and Leia making a family. Plus the main characters (Luke, Vader) have plenty of familial relationship too!
Pern - a whole bunch of families travel to a new world and establish a new society, which includes families, though some in an odd way based on the dragons.
Dune - Houses are families. It’s basically family vs family war here.
Foundation series - this is more a societal tale then following a particular person, but there’s lots of families in there.
Schlock Mercenary - it’s a company of mercenaries. And yet, still, there’s several family-related plots, or even major characters starting a family.
Spacetrawler - yea, not much. Mostly just high sci-fi adventure fun.
Starship Troopers - yup, mostly just action.
Heinlein - lots of one-offs, and not much family in there.
Hyperion - not too much there.
Newer stuff rarely has traditional married mother-father families with children.