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.
Even though you can trade anonymously with bitcoin the government can always ask you about the source of your wealth.
Some institutions are even demanding the proof of transactions before one wants to buy a home, for example.
Their logic sounds like "isn't it weird that a homeless rapidly got so much money allowing him to buy real estate?".
So complete independence from the state is impossible, even with crypto.