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.
Right now one of the main problems and obstacles in the way of bitcoin to become a national currency is that you can obtain bitcoin only by buying it for the local currency as Dollar or whatever else.
No you are wrong, you can obtain bitcoins by just working on icos and you can earn cryptocurrency or altcoins at the end of the campaign since the reward is also decent enough to sustain your daily needs.