Kayley
For some people, it's not selfish, there's an actual reason, such as having a kitten or not having their cat 'snipped' yet. There's also some cases where the cat themselves don't want to go out. I adopted a cat a couple of years ago that had been abused by her owners and had been found with her kittens about to be crushed in a scrap yard, and now she refuses to leave the house no matter how many windows are open. However, there are some people that enjoy the company. Some people adopt or buy cats as a therapy pet, to help with a mental illness or to comfort them. Some of these people may not be in a good area for the cat to leave the house, and they may also need the cat around in case they start panicking or stressing. Not that I'm saying that cats should be locked in and condemned to life as a house cat, but it's not always for selfish reasons.
Ironic
I wouldn't say keeping a cat indoors is neccessarily selfish, depending on the circumstances.
Our cats have always been indoor/outdoor cats, but this is because they're fixed, and the only time they've ever left the yard is to follow us on walks. However, not all cats do this, and there's always the chance of them being injured, stolen, or lost. My grandfather lost his cats whenever coyotes moved into a grassy woodland area near his house.
Some cats also don't like being outdoors. One of our 5 enjoys being out the most because he was a stray kitten when we found him, but then another one of the 5 hasn't stepped foot outside since we've gotten her. Some cats just aren't a fan of the outdoors.
So I wouldn't say keeping a cat indoors is all that selfish; some people are aware of the dangers in their area, the cat might prefer being indoors, or the cat might have a medical condition keeping it inside. When we leave for longer than a few hours, or it looks like it may rain, we always make sure they're all indoors. It's really just a matter of preference.
Sabrina
Letting cats roam outside it more selfish than the opposite. Outdoor cats are much more likely to contract illnesses and/or get injured. A indoor house cats' average lifespan is 15 years while a outdoor cat is only 4-6 years. I would say those people are benefiting the cat more but keeping them inside.
Kimber
Many people won't let their cats go outside, but there are a few people out there who have feelings and thoughts similar to yours about letting cats outside. You would love the cat ranch, a residential house that had 7 cats living there at one point..the backyard had an acre of land with a fence going around it, so the kitties can outside whenever they'd like. The inside of the house had at least 4 cats litter boxes as well as ramps along the walls that kitties use all the time for transportation and play. The house was rather spacious and mostly quiet (sometimes music was played but otherwise very peaceful). I can't even count how many critters the cats have hunted and brought in. They eat on the table instead of the humans. They not only can go on the furniture but even some of their usual sleeping spots is on furniture. This house (the cat ranch) is where the cat rules the house and was made for them, because the cat caregiver loves the kitties so much. You would like it. :)
Bill
I have 3 cats and I let them roam outside whenever they want. It's healthy for them because they get to breath the fresh air and act like they aren't locked in a box 24/7. Some people might just be scared of letting they're cat out because they can't protect it when it goes out. I have lost some cats when they were crossing the road to a huge field and forest across the street. But I believe that many people are afraid of their cat getting lost and never coming back, or having it stolen. Hope this helped!