Why are stray cats forced to live in shelters?

Ok there are cats everywhere where i live. they're just all feral cats that go everywhere. you cant touch them or even get within 30 feet of them. nobody feeds them and they are just fine. cats are able to take care of themselves so im just wondering why do people catch feral cats that you will never be able to touch and tak them to a shelter where their just euthanized. why not let them stay wild and actually live their life? like on animal cops or somethin where there's hoarders with cats locked in the house that you can touch, why not open the doors and let them out instead of wasting their time and money by catching these wild cats and than killing them. i really wonder why people dont just let them live on their own. they fend for themselves just fine.