It mews and purrs. It has 4 legs a tail, long whiskers and two pointy ears on top of its head. Cats have steadily occupied the foot-space around humans for longer than any living human can remember, and maybe that’s part of the reason why they are so misunderstood. Very few have grown up around cats in their natural wild state and fewer still delved into the natural behaviour of the domestic cat.
DNA and anthropological evidence points towards the African Wildcat (Felis Lybica) being the most likely ancestor of our beloved pet felines some time around 9,000 years ago in the Fertile Crescent (then known as Upper and Lower Egypt, Phoenicia, Assyria and Mesopotamia). The Fertile Crescent has some of the earliest known evidence of farming and storage of grains. Once people started farming they could produce surplus crop to store for when drought hit hard. With storing grains came vermin. This new food source needed a predator. Enter the Wildcat.
Of course being a solitary hunter which fiercely guards its territory against other feline intruders, living in colonies was not an overnight adaptation but the African Wildcat seems to have beat the competition to the punch through natural selection favoring the bolder, less-flighty individuals. As nature dictates the niche needed to be occupied so the Wildcat moved in. Through its domestication cats retained their predatory traits because that need did not changed. They still needed to hunt for their food and their meals were still “for one” portions. When you are hunting for one you do not need a pack so forming strong familiar bonds isn’t all that useful. Diseases that normally were of little bother before due to the respectful distance they once kept from each other, now likely made a slight comeback. The best chance they had to survive in this new niche is if they could tolerate each other without conflict, thus minimizing stress and reducing exposure to disease.
At that point dogs had been around for some time, so cats domesticated themselves in an environment where natural predators were still an issue, and when you could be dinner you tend to watch your surroundings and keep to safety.
Fast-forward to today and what you have is a very diverse species with a remarkable ability to survive due to their retention of many wild-type traits and the acquisition of domesticated traits. As controlled breeding is a much more recent venture with cats (200 or so years) and many even today are free to choose their mates, cats more accurately have drifted in and out of various states of domestication, semi-domestication and feralness depending on the demands of their environment. We like to call this the 50 shades of cat. Some are social with other cats choosing to groom them and sleep next to them, while others are still very solitary and territorial. However, it remains a solitary hunter at heart and still needs to perform hunting routines, eats small regular meals and does not enjoy sharing them. You also have an animal which prefers vantage points where it can keep a lookout for predators and prefers to climb high where they cannot be easily reached. They mark safe spaces by rubbing their faces and scratching on surfaces to deposit pheromones they can sense when they return.They still have an innate need to move away from their places of comfort to defecate and then to cover it up to avoid being tracked and becoming dinner. This is backed up by current scientific knowledge of the cat through observation in the field of animal ethology and is not just the anecdotal conclusion from one person's personal experience.
Therefore, keeping even 12 cats together in an enclosure is going to be forcing at least some of them to live against their nature, neglecting their need for separation, raising their stress levels, increasing likelihood of conflict, which in turn leads to increased exposure to environmental pathogens (s.a. ringworm) and a weakened immunity to them. Obsessive cleaning to remove these pathogens is only going to stress them out more by removing the pheromones they marked the place with. Sadly this knowledge has not helped many cats living in hoarding situations because many prefer to continue holding on to their anthropomorphic views of cats or mistaking them for dogs or thinking that all cats are capable of the same social behaviour as that exceptional cat they met once.
Serpell, J. A., 2014. Domestication and history of the cat. In: D. C. Turner & P. Bateson, eds. The Domestic Cat: The biology of its bhevaiour. Cornwall: Cambridge, pp. 83-100.