Many people are self-centered, plain and simple. Add to that the ignorance that many people practice daily, and it is a recipe for disaster when you add a helpless animal into the equation. It becomes inconvenient, I geuss, for these low-lives to care for their snake properly.. maybe they see it as more of a trophy/status symbol than what it is; a breathing, living being.
I would bet though, that the biggest cause of this type of thing, is fear. People get a snake, then maybe get bitten a few times; they become too cowardly to admit that the snake is too much for them to handle, and neglec results. That, and many people are just too busy to own any sort of animal, though they think they still have a right to.. it is all so sad and I wish there were less of this type of thing.
I am not speaking against people who have a snake, maybe get bitten and fear the snake, or realize they have no time for it.. and decide to let it go to a person who can care for it properly; these people are truly intelligent.