I think this is attributed to the fact that the big animals have a lot of room to roam around instead of tiny little cages. (ordinarytraveler.com)
It's a whole city of little cages and boxes all set up for guinea pigs. (craftsalamode.com)
This is also a sad time to leave the city because Grandma, the cat I've been fostering, hasn't been adopted yet and I am worried we will have to give her back to the SPCA It makes me so sad to think that she will have to go back into a tiny little cage again. (spiceandsprout.com)