At a time where I see currencies moving away from cash to digital I think the reason is partly so that governments can control the flow of their currency more particularly for laundering. They can possibly gain more taxation from a cashless currency because cash cannot be fully traced. If i sell my car for cash to another individual the government dont get any revenue from that because it is not traceable.
So in a governments aim to control our money it will leave a big opening for bitcoin and other decentralised crypto to exist along with fiat and will allow people to "trade" anonymously with each other over a completely independent infrastructure.
Bitcoin is peer to peer transaction and i think its untraceable. We dont know the identity wallet owner. For government, this can not trace to collect taxes but if we use bitcoin in merchant, government can collect taxes from VAT
Yes, I also think that the taxes will be collected, but Bitcoin will be used almost everywhere. Each one, who thinks that the cryptocurrency if more convenient than fiat to him, will operate with it.
Governments are going to have a lot of trouble trying to get taxes out of people that use cryptocurrencies because they will not know the identity of the people that make those transactions and if they decide to put a law in place that forces you to identify yourself many will choose to ignore it because they will be happy to sell their products for bitcoin when they finally understand that selling for bitcoin and holding it is one of the best things they can do for the long term.
Because if they do that and bitcoin skyrockets as we know it will happen then the benefits they will get out of it will be many times over whatever fiat they could have received by those products.