It seems to be a prevailing joke in Rick and Morty that the often-alien antagonists frequently have domestic families and lives that even humanize these supposed antagonists. Even the Freddy Kuger-esque dreamscape killer has a quaint domestic life.
In some ways, it also reminds us that these creatures have stakes too. It parallels in some way to Rick’s family man status. Rick, though a sociopathic, self-centered scientist, is also a family man. How does the existence of their domestic lives ultimately cement how chaotic and complex the multi-verse is and mirror upon Rick’s domestic life?
This is really interesting, I never thought about it much until now but you are right, they give a lot of antagonists backstories. A good way to look at it in a neutral way is that it promotes the idea "we do things for others." Although Rick is selfish he cares deeply about Morty and his happiness as seen in him killing the Jelly Bean King that sexually harassed Morty. It's an easy thesis to support considering the end of season 1 Rick gives up the Wubalubadubdub phrase when he finds fulfillment in being with his grandchildren. – Slaidey7 years ago