If crypto does gain massive adoption and you are able to pay for things in crypto, there would be less of a reason for people to cash out into fiat. How would government collect taxes from crypto gains then? Also, if something like ETH becomes big, how is the government gonna stop people from making pyramids, ponzis, and scams in general?
This probably why government still not implementing the usage of cryptos. This is one factor they are considering, that is why most of the countries still not open of having cryptos as their main way to use in payment physical or online. The process will take a lot of studies and debates just to pursue the crypto payment. Also, the security of it is also in question. Most of the hackers will also find ways just to take the advantage of getting the access of our wallets. So many answered in this topic, so i hope somehow enlighthen us.