I read an article that was admittedly about Spam scams, but I'd imagine the same would apply here. They're intentionally designed to be off-the-wall and unbelievable. That way, they know anyone they rope in is likely to be gullible enough to go all the way and fall for it without much problem. They don't want to try to make something super-believable that will cause smart or smart-enough people to question it and spend a bunch of time researching, because it wastes their time when they drop out.
Unfortunately, this often means elderly folks get the worst of it, though apparently college kids are getting hit too.
In fact, here it is