Volatility, Loss of Capital, Transaction Problems (History of high fees and long waiting time), better alternatives (Paypal for fast transactions, Gold/Stocks for long term investing)
these are the main points that into my mind.
Also, the hype in december was just because EVERYBODY could make money. Right now the market is shit thats why they arent investing. Maybe they will jump back at the bangwagon when we make higher highs (12k and +20k)