All of the transparent block chains create another problem, however: Pervasive surveillance, and chilling effects. For that reason, I like the singular cryptocurrency which offers the anonymity and fungibility of cash, without a pre-mine scam or a graft tax, Monero. I think it is the only exemplar which offers all of the features required to serve as both a store of wealth and a medium of exchange. (Privacy being a requirement for fungibility.)
Sending value anywhere in the world in a very short amount of time without having to trust a middleman.
That's what cryptocurrencies could offer.
That alone could be a reason too. My other guesses: versatility and in some countries ease of use when compared to standard solutions.
It's the hot new thing, there's a frontrunner but not an established winner, and investors are still willing to give people money for it.