It didn’t always work that way in those days. It was not a huge number of cats.
Ranch and country life is/was different.
Our Vet drove 60 miles to visit and I don’t think he spayed cats.
All vets spay and neuter. I realize it might be different on ranches and that ferals become real predators. But the idea of a vet killing a cat? Don’t like it and she’s already been fired.