Why make it illegal if you could just regulate it and get taxes from people who make money with Bitcoin?
That's a whole lot of revenue for the government that they would be missing out on if made illegal.
But Bitcoin is actually also illegal in a couple of countries:
https://atozforex.com/news/top-countries-where-bitcoin-is-illegal/I agree that they could not regulate the taxes becuase bitocin is decentralized and governments think that bitcoin is a scam even though its not a scam. In addition to that, I think that using bitcoin is a tax free. Lastly, I hope bitcoin will be illegal in all country in the world.
Legally speaking, some countries tax your bitcoin and not disclosing possession is tax fraud. It is up to the individual user if they think they can get away with it.