Every combination of two or more human beings has both a useful aspect and a political aspect. These tend to conflict with each other. As the political aspect becomes more and more influential, the organization ceases to be useful to its members and starts using them.
Why does this happen? Because the better an organization is at fulfilling its purpose, the more it attracts people who see the organization as an opportunity to advance themselves.
The ability to get ahead in an organization is simply another talent, like the ability to play chess, paint pictures, do coronary bypass operations or pick pockets. There are some people who are extraordinarily good at manipulating organizations to serve their own ends. The Russians, who have suffered under such people for centuries, have a name for them -- apparatchiks. It was an observer of apparatchiks who coined the maxim, "The scum rises to the top."
I'm not by any means the first to observe that libertarian political organizations tend to make even less headway toward fulfilling their purposes than other types of organizations before getting drunk on their own apparatchikism, falling down and passing out in the vomit.
Solutions? I haven't found them yet, but doing so is an ongoing project I take a good deal of interest in. Some of the ideas I put into the Boston Tea Party's scheme of organization were intended to test the idea of an "apparatchik quarantine" which would retard the concentration of power in "leadership" and keep activism under the control of activists. Jury's still out on that one, in my opinion, but surprises of both varieties (pleasant and unpleasant) have abounded.