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,”