When you think of the sort of pet that people can be truly emotionally attached to, chances are *really* good you’ll think of either “cat” or “dog.” Any species other than those two, at least in the US, will either be far fewer in number or far less likely to be something you really bond with. A goldfish, after all, is more likely to be something more of a decoration than an entity you empathize with.
Me, I’ve had cats, dogs, ferrets. Bonded with all, mourned those who’ve died or left. I also had some Triops, some big brine shrimp sorta prehistoric monster critters; when they died, it was a disappointment, but not mournful. I’ve never had pet bunnies or sheep, but I’ve met such critters. Cute enough, but… meh. No connection. Why not? Because there was “nothing behind the eyes,” one might say. And… because bunnies and sheep are quite different from humans. They do not hunt. They have no “killer instinct.” They are… different from us.
Look at the natural world: the creatures we think of as being “smart” or ‘high up on the evolutionary ladder” tend to be vicious killers. Chimpanzees? Sure, they’re cute (-ish) when they’re young, but as adults they’re 600-pound murder machines who will rip your limbs, face and nads off. Dolphins? Sure, Flipper looks cute, but they will murder other species of dolphins apparently for fun. Orcas? OK, the alternate name of “killer whale” kinds gives it away, but they’re well known to play with their food. And their food tends to cute cute, fluffy-bunny seals.
Of course, “smart” isn’t exclusively the province of predators. Elephants are well known to be quite smart, with complex emotions. But… you tick off an elephant, and they turn into *giant* murder machines. They might not eat you, but they’ll kill you, and not purely for defense. They will attack other creatures simply because they’re ticked off.
So… being killers seems to correlate with making good pets… and with making them understandable. Of course it’s not a 100% match; go head and snuggle up with a shark if you want, won’t get you anywhere.