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.
Personally I think that another reason is that simply many people are not really ready to be completely responsible for their own money and they are afraid of something like bitcoin.
After all a huge deal of money is stolen from credit and debit cards all over the world, and those people depend on the banks to save them and recover their money, but this is not possible with bitcoin, so since people do not know how to take care of their coins I think that we are bound to see a massive amount of money being stolen if bitcoin was adopted massively, and then once they lose their money this way those people will criticize bitcoin for its inability to reverse transactions, even if that is a feature and not a bug.