Because there's garbage, water, shelter, and safety in sewers. What more could
they want?
sewers
You can often find rats living in sewers, but that's not the only place they live. They can also live on the streets, especially dirty areas, in the country, in homes.. basically anywhere. Eww..
Actually, the sewer people mate with rats to make Ratmen, who then live in the sewers. So, there is more ratmen.
RATS
Same as they do in a house or office
You can buy cheep fuzzy rats in the sewers
Garbage dumps, sewers and anywhere they can find shelter away from the eyes of people and other predators.
Yes they do. Quite abundantly in the sewers. Most are infected so stay away from any rat you see in the street.
You can find these Hell Rats in the sewers in Varrock, You can find Varrock by exploring your map, have fun.
rats, garbage, poop
Wild rats carry fleas and disease. Not consciously of course. But because of how they live, in sewers and basements. Domestic or "pet" rats are very clean and rarely carry parasites unless exposed to them via other pets like cats and dogs.
There are 64 different species of rat. These range from rats that can be kept as pets to rats that live in the wild in sewers and wharves.