In think it's personnel selection.

I think the militias don't get the top-of-the-line retired military people. They get the wannabes, the people who love the trappings of being tough and deadly, without the actual skills or training. Putting on my amateur psychologist's hat, I'd guess that the militia types mostly washed out in the military, but are still looking for what they went into the military to try to find - a sense of belonging and identity.

The real SEAL/Delta level people don't go into a militia to try to find that - they found it for real in the real military.