I think it's mostly the volatility that scares investors. The information/technical skill required to start up scares users. That and the fact that many noobs lose access to wallets by accident and just lose coins. I guess you could say that you can lose cash, as well, but cash doesn't have the threat of getting hacked. Again, I guess cash can get stolen, too, but people fear the unknown. If you don't understand how something was hacked, it's scarier than getting mugged because at least they know how to learn from that experience.