I used to be a very active member of two organizations, an international one and a local special-interest group. I attended meetings regularly, held key volunteer posts, and contributed to publications. Years ago I became inactive in one, and last year I dropped out of the other.
The main reason was the same in both cases: politics. I have no interest in the fights and the jockeying for influence that go on. When bad leadership moves in and drags the group into pointless, destructive struggles, I move out.