People do this because of a perception that pets are disposable. They get something because they think it would be cool then dump it when they realize they're in over their heads. Or they had to move and couldn't take it, or any other number of excuses. And before you say give it to someone or a rescue, remember that there aren't a lot of people that can just take a large snake, and rescues usually want money to cover a vet visit. Much easier in these idiots mind to just dump the problem in the trash.