Well, I'm not sure what you mean by "many forms of anarchy..." there's only one "form of anarchy..." just as there is only one "form of government" ... I would figure all those opposed to statism, illegitimate (based upon the non-aggression principle and the concept of individual sovereignty) claims of "authority", "the government," and "involuntarism"/coercion/the initiation of violence would be anarchists.. anarchy is "no rulers," if there's only one way to not rule others, to not be ruled, then there's only one "form of anarchy"..
im not sure if youre asking "why dont the seemingly different 'factions' of 'anarchism' coordinate for a common goal' with the 'why not?' but it's kind of like aksing "what's the perfect chair look like?" how could anyone but the individual know why they do not coordinate?
the issue here is a belief in "authority," which is instilled via the "school system" from an early age. it's not so much "the state" as it is the people who believe in "the state," that is the core.. aside from going off and trying to avoid 'the state' at all costs, finding a place to live as free as you can, nothing will change regarding 'the state' until the individuals who believe in 'the state' give up the myth, or when enough people wake up and begin resisting/refusing to comply...