Same reason you see so many rabbits on there after easter, or any other pet for that matter.
Sounds cool in theory, but then when they get the animal they realize it's actual work to keep/care for it. Yuck, can't be having to do any sort of work, won't it feed and clean up after itself?!? Our society has somewhere decided that animals are disposable.
Not everyone of course. There *are* legitimate reasons for rehoming animals, and then there are those who'd never dream of giving up pets.