Why do people dump cats and can I help to prevent that from happening?

The house I’ve lived in for the past 6 years house backs onto a state park where people dump cats. In this park there are predators like the Fisher Cat (a weasel), and a bob cat has been spotted recently. People can’t have indoor/outdoor cats here as they wouldn’t be safe. I rescue those I can, get them shots, neutered and rehomed. I’ve rehomed all 14 of the ones I rescued, but then there are the ones I couldn’t. How could people do that, and how can I help to prevent that from happening?