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.
No, you are wrong in many ways. The existing financial system in the states is well regulated and quite suits the current governments. On the contrary, the introduction of cryptocurrency is not profitable for them, because it is the decentralized cryptocurrency that they cannot control. They can allow the circulation of cryptocurrency on their territory, but they will not actively support it.
Governments will never give up their national money.