I've purchased a few altcoins with differentiation and solid dev teams behind them. And it's still a gamble; I expect most to die off.
Same reason people buy deep out of the money call options or do leveraged FX trading - they just like to gamble. The whole FX brokerage business (and that includes crypto) is basically run like a casino.
They created a Counter-Strike "lottery" website and uploaded a lot of videos of themselves winning big, while never disclosing that they were the secret owners of the site. Of course, their supposed recorded lottery winnings were staged as a way to drive traffic and money to the site.
From the Willy bot through to the latest ICO craze, the whole cryptocurrency scene is riddled with people engaging in pumping prices - which means that any reverses in price hit sentiment hard and cause price shocks, something I think we're going to be seeing a lot more of over the next year or so...