Because not all flavors prefer that term, since it has negative connotations in certain circles.  It's also not literally accurate, since it literally means "no government" and not "self government".  Any particular individual can either govern himself, or he cannot.  He may not have ever been taught to govern himself, as is the present case with way too many publicly educated Americans; or he may have simply never accepted basic mores with which to govern himself with; or he simply may be mentally incapable of reliablely governing himself.  I can certainly accept that 98+% of the adult population is capable of self-governance from the age of reason (roughly 12, depending upon the person) till either death or senility, but it cannot be argued that those people actually will.  In a truly anarchist/libertarian/minimalist/volunteerist society, most crimes today won't be crimes and the crimes that remain will have immediate and permanent effects upon the violator; so it's not hard to imagine a society with a vanishingly small incidence of violent crime simply due to Darwinistic 'survival-of-the-least-offensive' forces.  Still, there will always be that vanishingly small percentage of people who are actually incapable of reliable self-governance, which is why I consider a truly anarchist society (The Probability Broach) to be impossible.  A more likely outcome would be voluntary self-identification, such as the 'phyles' concept (The Diamond Age).  Either way, we can't get there from here, so at some point we are going to have to transition through a harsh period of hightened suffering and violence, (Alongside Night) which is exactly the condition that Karl Marx suggested would be the best opprotunity for socialists to change the nature of socity itself into his dream world.  Obviously, history shows us that socialism doesn't work, but that same history also shows us that such retoric does work, if the true goal is snatching of power by a core of like minded sociopaths.  If any minimalist society is to ever become real, it's only possible if by a deliberate plan involving years of education and development.  Periods of civil unrest are unlikely to result in a peaceful & anarchist society and are very likely to result in a dictator (in fact, although not likely in name).