I mean, running a competent, centralized organization where the top clearly controls the lower levels and knows what’s going on would seem somewhat dangerous if you’re running an underground terrorist organization, because there’s a very high chance the leadership of such an group will get targeted, and since they will have fewer resources than their opponent, theres a good chance that leadership will eventually end up captured or killed. If the rest of the organization relies on the top, or the top knows where and who the members all are, then this will probably destroy the organization. So, there’s incentive for such an organization to be distributed and decentralized to some extent. Further, it won’t be staffed by highly trained professionals, but by whoever can be sufficiently motivated to join it, which isn’t going to lead to a high degree of competence, just zealotry.