In addition to the fact that some countries set Bitcoin as legal tender
Only El Salvador has made bitcoin a legal tender, no other country for now, but it will be great if other countries can do so as well.
and some countries prohibit participation, which will also cause Bitcoin to plummet.
Did you noticed bitcoin was not affect in price when El Salvador made it a legal tender while the news about the ban in China plummeted the price, it depends.
What other factors will cause Bitcoin to skyrocket?
I have noticed recently that bitcoin price is correlating to US index, also there are many good news that increase the price while many bad news that decrease its price, there are times that people also just buy bitcoin, especially when the price has plummeted to a large extent.