If we dare to face the truth, the idea of bitcoin becoming a legitimate global currency is really a pipe dream. Governments will never accept a currency they cannot control and they have no shortage of better solutions. There is no reason for them to favor a currency they did not create and cannot control.
Additionally, bitcoin has too many limitations to be a currency as it can only process 7-10 transactions per second, which is too slow compared to traditional payment systems like Visa or MasterCard, let alone compared to altcoins.
Given Bitcoin's decentralized nature and security, it is more suitable as a store of value, an asset like gold.
The primary reason why governments are not willing to adopt decentralized Bitcoin is because they don't have any control over that financial system. It's really that simple.
For centuries, every government has full full control over financial system of the country through fiat system. The reason why government likes Fiat currency is because they not only control it but they can also manipulate it according to their requirement.
As far as limitations of Bitcoin like scalability is concerned, we have fix for them available in the form of LN. But that's secondary issue.