A shorthaired cat can get mats and some longhaired cats can be pretty mat-free, it just depends on how much undercoat the cat has. Sloughing off a lot of dander can also contribute to matting. Being overweight can decrease a cat's accessibility to certain areas when grooming and that can do it. And age with or without illness can cause a cat to neglect grooming, and that can do it.

One of my kitties mats. He's older, but he's matted for years. He isn't overweight. My vet says he has a coat like an Abyssinian--apparently they have a lot of undercoat. My Pistol has TONS of undercoat! And he's always had lots of dander too. I put a little bit of salmon oil on his food every day--my vet says this might cut down on the dander. I think it's working. I'm seeing less dander and smaller mats. Unfortunately I'm not seeing NO mats! Also unfortunately, this kitty HATES being combed or brushed! So I have to get the mats one at a time. I keep a cat comb handy in the living room and whenever the opportunity presents itself, I get him on the fly! Whoosh! One more mat combed out. You just have to do the best you can.