Same reason I don't put my money on the ponies. I have no experience at speculation and no confidence that I could do a good job of it. I'm pretty confident that every cryptocurrency bubble will burst in the near future, but I have no idea when this will happen and no confidence I will get my money out in time.

And I have serious moral objections to all existing cryptocurrencies. I'm not going to support something I consider immensely harmful as a get-rich-quick scheme.