I have been an animal advocate and still belong to the "no kill shelter" (as a contributor) "The Animal Umbrella". The volunteers feed, trap, provide medical help and find new homes for the abandoned cats. They rely on donations, sometimes the money is not there and the volunteers have to pay out of their own pockets to feed the cats.
In many institutions, there are a lot of cats that have been thrown out of people's cars and regularly the animal control comes in and the cats are euthanized. There are millions of cats like that - we save one cat at a time but at the end, many, many, cats have been saved.