Because, if you have so many pets at home you can't spend so much time on each pet. The other reason is they are messy, they messed up things like books, etc. Sometimes they are dangerous for pregnant women. Sometimes they become aggressive, last year in USA 4.2 million people got bitten by pets.
Of course there should be a restriction on how many pets you can have. It should be around five pets. This is because if someone has 20 cats in 1 house it's just not going to work out for many different reasons. Firstly, the house will be a mess, I have 3 cats, I know what it's like. Secondly, the house will be covered in cat droppings and will have a bad smell. Finally, in the end the owner will realize that they cannot cope with 20 cats and will end up abandoning the cats and the cats will live in their own mess.
There are usually restrictions on the number of dogs you can own in cities where people live close together and share parks, sidewalks, etc. If you live in a rural area, you usually can have as many dogs or cats as you want, as long as they are not a nuisance. Fish don’t really get counted as pets that can cause a public nuisance, so you can have as many as you want.
Almost all cities have leash laws for dogs; many have leash laws for cats. It is usually against the law to let your dog(s) run freely, especially in public parks and recreational areas. It is against the law for you to have outdoors cats in areas that have cat leash laws. http://doglaw.hugpug.com/doglaw_008.html
Taking care of more than one cat and a dog is difficult. And, by taking care of I mean, the proper yearly medical examinations, grooming of the animals, exercising, feeding, and waste removal. If you have more than one cat, you will probably need to change cat litter quite frequently, or your house will reek of cat urine and dropping – a disgusting smell. And, if you don’t get your male cats fixed at an early age, they will spray – good luck getting that smell out of your house or apartment. That is why many apartments do not allow cats or dogs. And, if you cat is not declawed (front paws), they will destroy you furniture, and wood posts (e.g., stair railing posts), even if you have a scratching post. I have owned over 20 cats and know this for a fact.
Many people who own animals believe they don’t need yearly medical examinations, and don’t bother. Even, though most cities have laws requiring yearly vaccinations, e.g., rabies.
Many people walk their dogs in public areas and don’t pick up their waste, because they don’t give a crap (pun intended) about other people’ rights. They are just rude narcissist jerks that should move out into the wilderness and live alone, preferably leaving their pets to decent responsible people.
My boyfriends parent has over 40 rabbits and more pets of different nAtures but I honestly don't see why because his parents spend most of there money of the pets and their house constantly smells , there garden is full of mud because all the rabbits have eaten it and now the rabbits arnt getting any grass anymore , she may like animals but what is the point of having more than 50 ....
In the United States, we should have the freedom to choose this sort of thing. I agree with glasspotfull that if you are renting or subletting, then you should be bound to the rules of the landlord. Pets can be a mess and overwhelming. However, if it is your own private property you should be free to do with it as you choose.
Except in the case where the occupant is a renter (bound to a landlord), there should be no limit on the amount of pets someone may have in their home. Owning a large number of pets do not harm other individuals; there is no basis for making the activity illegal. It is the right of the owner to own as many pets as he/she would like.
If you have more than a set number of animals then a special permit could be required. This permit should only be approved and annually renewed once your vet has signed off on it stating that you have sought regular & routine care for your pets. Also a letter from a neighbor or signature stating that they do not object could be useful.