I’m very sorry to hear that about your friend and experience. And thank you for your service!
But the answer is simple: it’s a cult. They are brainwashed (and ironically think everyone else are the ones brainwashed). So it doesn’t make sense and they just ignore that or have cognitive dissonance.
And unfortunately it’s just very difficult to dismantle a cult. Just look at scientology/mormonism/jw/etc.