Because the world is more complex than simply one community forming an anarchist collective and then suddenly all groups of people are involved some harmonious syndicalism where everyone agrees on a basic set of standard social norms and ethical behavior.

You might form an anarchist commune, and maybe a few miles away a remnant of the Hells Angels forms a white supremacist commune based on their own organizational structure. If they decide they want to attack and take your resources, you need a viable means of common defense. Which implies some form of social organization.

If there's an overarching government, if it's well-designed and effective, with the correct goals and priorities, then it should at a bare minimum protect against basic things like violence, theft, extortion, racketeering, abduction, and human trafficking.

And if your commune is powerful enough that it decides to be the one to enforce those norms, then it is a de facto government, no matter how decentralized you try to make it.

what if they just take the resources since they're stronger and greater in number?