There are diseases they can catch from other cats, get infected from cat fights and run into humans that lack a heart for our cats and kittens. They can be run over, stolen or be killed for the sport of it. The list goes on. Even indoors, felines need our help if they're to live wholesome lives. There's the issue of good nutrition, protection from poisonous plants and poisons in general, needed attention and interaction and good grooming.
Some people think hairballs come with the territory, and to some extent, they're right.
But we owners can do a lot to minimize our cats discomfort by simple grooming. I made it part of my 'undivided attention' periods with Buckwheat. In fact, he sometimes manipulated me with his eyes and purring into forgetting about time. Please remember, that in some ways, I'm just like you. I flourish on love, adore praise, and love having both playful and lovey-dovey times with you.