1. a big factor is : legal issue. it is not legal and not acceptable in all country.
2. also some people scare because bitcoin is not commodity, nor currency.
3. Prone to illegal activity
As we know due to the lack of government control, terrorists and extortionists are also utilising the cryptocurrency space to their advantage. Bitcoins users on either end of a transaction can remain relatively anonymous and cybercriminals have found ways to mask their addresses, so it can be difficult for government authorities and companies to trace such illegal activities,
People are scare to invest in bitcoin, primarily because of ignorance. If we knows all about the pros and cons of it then it will not become a danger to invest in bitcoin. As long as we know that how it works amd legality of the bitcoin in our country, we will not become fear to invest in BTC.