Imo, there are 3 main reasons acting as barrier for worldwide adoption of bitcoin:
Regulations
Volatility
Security
These three things actually have their own criteria and descriptions. Because in terms of security, Bitcoin is clearly very safe to be used by anyone even though it can't be used for all purposes and for Volatility it's also not so bad even though it had experienced bigger changes in a certain period. However, for regulation, I think it clearly needs to be adjusted again because every country in the world already has its own rules which are generally used by citizens of their respective countries.