3. Fluctuating value: The value of bitcoin isn't steady as it rises and falls. The uncertainty in the price and value greatly hinders the general adoption worldwide.
4. Awareness: Nearly not enough effort on creating and spreading positive awareness on it as some government and individuals alike is hell bent on spreading negativity around and poisoning the minds of prospective users. People need to be aware and understand what bitcoin is really about and be awake to its uses.
Those two points are a major cause in my opinion. I would also add that buying a bitcoin is not exactly a straight forwarding thing to do since usually you have to open an account on an exchange, send the documents, wait to be verified, transfer the money and then decide where to store them. Many times when you explain to people all these steps, a lot of them immediately think it's too much effort.