Some factors may be the that people are afraid of the security issues pertaining to it and also they think their monies are going to be stolen when they invest into it.
One of the factors that scare others is its legality for bitcoin is not used world wide infact there are still countries that banned the use of bitcoin. Also they are scared to be scammed as we all know that scammers are everywhere and even in bitcoin there are people will do anything for easy money.