Despite the massive growth, advancement and advantages of Bitcoin and most crypto currency, why is it hard for most countries to fully accept it is or permit it's exchange?
Because Bitcoin isn't purely used as a currency. It was primarily being used as an investment.
Any investment is always tagged at risk in any country. And the fact that it's volatile makes it riskier.
Just enjoy, at least, that most countries accept bitcoin even though not tagged as a legal tender.