I have worked for many years in the pet industry, and I have kept, as pets, a total of 63 different species of animals. (Currently, I live in a one species household.)
As manager of one of Chicago’s oldest and largest pet stores, I had the opportunity (or misfortune) to participate in this conversations a seemingly infinite number of times:
Parent: “My son Idiot Boy wants a pet, but we want something unusual: not just a cat or a dog. But I want it to be low maintenance.”
This was my cue to hold their head under water until they stopped twitching, and then I would explain to their stiffening corpse: “The reason cats and dogs are such popular pets, when compared to say porcupines and sea slugs, is that they fit in better with a human household than any other animals. They respond to affection with affection, and their own lifestyle is more easily adaptable to and compatible with that of a human companion.”
A brief list of counterexamples of the second-tier pets (Leaving out such things as horses as pigs, as my customers were all urbanites.):[ul][li]Ferrets smell bad, sometimes bite, are difficult to litter train, must live in a cage most of the time, and only live three years.[/li][li]Ditto most other small mammals, with varying degrees of odoriferosity and lifespan.[/li][li]Iguanas aren’t really capable of affectionate response, are difficult to find a competent vet for, are with extremely rare exception difficult to potty train, require an investment in equipment, space, and herpetological education.[/li][li]Ditto other lizard species, except the Green Iguana is the closest you’ll ever find to a lizard capable of affection (though I had a Varanus dumerilii once that I wondered about).[/li][li]Snakes are very easy to keep and require very little space and equipment, but are incapable of affectionate interaction.[/li][li]Birds are good, especially some of the larger ones, but they demand a great deal of attention and relatively deep pockets, vet and equipment wise.[/li][li]Fish, with few exceptions, aren’t really pets, but more an aesthetic or scientific installation, that require a constant supply of money and attention.[/li][li]Turtles share with other reptiles expense of vet care, plus major investments in equipment and education.[/li][li]Tortoises can usually do with less equipment than turtles, but need even more education; plus very, very few species of tortoise are available in the pet trade, and those that are can be extremely expensive.[/li][li]What have I left out?[/ul][/li]
This is not to say each of these animals can be a rewarding “pet” in its own way, only that cats and dogs are still the pets we’ve come up with. I was usually able to convince them that if they were afraid of a commitment to a cat or dog, then a more exotic pet–which, as a rule of thumb, are often more of a hobby than a companion–was probably not a good idea.