It has everything to do with this bubble. If there is no stability of the underlying token, and no places to get low risk interest, and no easy way to spend the token in the outside world, well what else is left?

If you have ETH one of the few things you can do for it to earn more is ICOs. You don't have the ability to buy real estate in the real world with it, or buy real shares in real companies with it. You can't really do much anything except what people are doing with the ICOs.