Cryptocurrencies are special in that, almost from their very inception, they could be used to make money. There are at least four ways one can make money with them: those with access to cheap electricity and enough starting capital can literally print money out of thin air; they form unregulated exchanges to gamble on; they're very useful for scamming people; they're also useful for laundering money and buying illicit goods. These four things give cryptocurrencies a lot of interest and participants.