It just is.
Capitalism is exploitative and hierarchical by it's nature.
It exploits others, involves private ownership of the means of production, necessitating bosses and it creates monopolies . Anarchism is against all forms of hierarchy,exploitation and coercion. one of the main principles of capitalism is the making of profits above all else. it is greedy and manipulative and cannot exist without a state. It requires private property (which is theft), subsidies and protection by the state and therefore goes against anarchism. Anarchism is not just about abolishing the state. Abolishing the government is a very very important feature to Anarchism, but it's not the be-all-and -end-all of everything.
I can't stand how they (and some other people) assume that if you are a market anarchist, you are somehow automaticaly a capitalist. horsefeathers. it is perfectly possible to be pro-market but anti-capitalism. mutualism is a good example of how this could be done. it is my contention that so called "anarcho"-capitalists are esentially small-state libertarians (minarchists) who are in denial.
Inspired by George Carlin, I'm going to make a list of people or ideas I could do without. this will take me a while so I don't know when it will appear. I will not order it in any particular way just randomly. I may do another along opposite (ie positive) lines. whatch this space.