Because we don't enough infrastructure in place that could govern people on its own. It is a wild dream to believe that at this point in time we would be able to govern every aspect of like without having any government at all. I am not saying it will never be possible, but I believe there will also be some sort of governing body. Imagine in how many countries the military may decide to overtake control? It is not as easy as you think to just live without government.
I have never thought of living without a government because all the people in this world are in their respective countries with different systems of government so that the rules will always be different even though they have a body that will regulate this, so it is clear that all things will not be easy to happen although it is easy when it is said.