Xenomorphs are just not good around the house. Sure, they grow fast and you don’t have to feed them. But even a domesticated Xenomorph (if that’s even possible) can be a lot of trouble.
For one thing, they bleed acid. Say one accidentally breaks a tentacle; you end up with a big, stinky, acid-burned mess. And they tend to be most disagreeable with other living creatures, regardless of species or genres.