why are there so many different definitions of anarchy?

Answer 1

there is no single foundational voice for anarchist thought (and some of the most influential thinkers said some apparently conflicting things, like bakunin), so there is a lot of flexibility left for people to find and focus on the person, or the ideas, that most appeal to them. this is aided by the idea that anarchists promote people finding their own answers, so that decentralization and a million different trajectories are both desirable and inevitable.
this leads to people calling themselves anarchists who disagree intensely (and sometimes widely) with each other, and an inherent weakness of the label "anarchist" (since calling one's self that doesn't actually mean that anyone can make assumptions about what one thinks), which actually makes the label not as pernicious as other labels.