This is about regulations for businesses and entrepreneurs. Yes I know that in countries that prohibit Bitcoin use, they (Bitcoin users) can still receive and send Bitcoin. However for businesses and companies, they will be monitored by the government. If the local government does not allow the use of Bitcoin as legal tender for their business, they must comply. Violations can result in sanctions or even bankruptcy, as the government is ruthless.
The bottom line is regulation.
Regulation can be considered as the biggest barrier preventing businesses from accepting bitcoin as they need to strictly comply with government regulations. But that's not the only hurdle businesses face, there are other challenges like volatility, not many customers use bitcoin for payments. That is why many countries have allowed the use of bitcoin as a means of payment, but many businesses still do not accept bitcoin.
Although bitcoin is not legal tender, it can be used as a means of payment in Australia, Canada, Slovenia and many other countries. But according to many surveys, not many businesses accept bitcoin yet.
https://nowpayments.io/blog/countries-that-accept-bitcoin-as-a-payment