ALF was set before the TV series, in which Gordon Shumway explained that his planet exploded. So all of those family members you get to know? Dead.
Denver: The Last Dinosaur
Once again, he is the last of the dinosaurs. It doesn’t even want to be subtle about it.
A small group of 400 humans flee from their conquered homeworld into Earths prehistoric past. 400!
Disney’s Gummi Bears
Where exactly are all the other Gummi Bears? The show says they fled the land. Sure.
Gargamel was constantly trying to eat them, or at least do something to them. Either way, the villian wanted to wipe out the title characters.
Aside from the Thundercats themselves, everyone else from their planet of Thundera are killed in the first episode.
Where do I start? How about Unicron eats planets full of robots!