I think it maybe has something to with its great instability and the market is influenced by many factors which is not that easy to master the trends and determine when to buy and sell. And the other factor is security related, as you can see a lot of money has been stolen or lost as a result of the improper handling of the private keys. As cryptocurrency to a large extent is still relatively new to a large number of people, they may don't know how to keep their assets in a secure way! And the other thing is it is a 24-hour trading market with no limited to ups and downs, so people may end up losing all their money waking up in the morning!