Anarchy does not mean absence of organisation. It means absence of unfair dominance and control of one over another. An anarchist society could be highly organised, in all kinds of ways people decide to.
At least on-line, the definitions I'm seeing are very heavy on the "there are no rulers / authorities / states / government" points. There ain't no "as long as it's fair" escape clauses.
Small-scale, if well-behaved people are the vast majority, and there are easy ways to cut out the occasional bad actor - that can work very well. Just look at the Internet of the 1970's and 1980's.
Larger scale, with a real-world mix of human behaviors, and cutting off the "wrong sort" far more difficult - OOPS. Look at the modern internet, and the many toxic actors and organizations that have explosively grown in the large-scale anarchy.
EDIT: Add "no big rewards for becoming dominant" to my preconditions for anarchy working well. You for-sure could not have gotten Zuckerbucks-grade rich by dominating the early internet.
