What is holding back is definitely from constituted authority
Was there no constituted authorities when El-Salvador adopted bitcoin as a legal tender, then after some time, Central African Republic also join the same step by making it decision, this is more of a personal choice and policies each country is facing internally, because bitcoin is a decentralized digital currency and you don't expect any country law or regulation to override on its adoption.
What is stopping it's gradual integration?
Indecision
Fear
Misconception
These above are what is making some countries yet to have a stand on bitcoin adoption as a legal tender.