Followers are currency on twitter for a lot of people - you don't have any real relationship with them, just having many of them increases your swagger. So, play a silly game using your followers as play money - if we play and I win, they end up following me instead of you. If you played carefully and diligently enough, I suppose you could end up having more followers than (someone famous), all of whom are following you with no real idea why.
It's silly, and it pretty much says to your followers that you consider them disposable minions, fit for nothing more than to be wagered away in games of chance, because you are such a badass. Inexplicably, many people find this exciting and admirable, at least as long as you keep winning.
As you can probably gues, I like it...in fact this strikes me as a good reason to spend more time on Twitter. I guess it appeals to the unfulfilled megalomaniac in me :)