Cryptocurrency doesnt really have tax, so if the government just allow it, soon it will become the citizens' source of income. If that were to happen, the government wont have money for economic purposes. Sometimes the banning of bitcoin may solve issue to a country's bankruptcy. Their banks that allow cryptocurency in their own place but that is only for 3rd world countries. If a country can make infrastructures for crypto mining, then tax wont be a problem anymore.
a country needs tax to be able to fund their Health, education, transport etc. systems.
if for instance a country started to tax mining it would have to be regulated and this
goes against what crypto is about.
also if countries taxed mining, miners would just pass those taxes down the line to
transactions in the form of fees, as in fees will increase. not good and its not going
to happen anyway.