Probably too embarrassed to admit that it's true and too fearful to renounce the perp who still prompts the swing of the scimitar from the grave against those who do.
It is also entirely possible that they feel they have no reason to renounce anything, feeling fully justified in committing atrocities against the human race. After all, if their 'god' says it's okay, who are they to argue?
How do you convince someone that they have a terminal disease and need help when they are feeling euphoric and invincible -- especially when they have already rejected the only medicine that will save their lives? (Doesn't Islam teach that they have no need of a savior, rejecting the concept of sin, guilt, contrition, repentance, atonement, visitation, redemption, and Grace?)
Do the 'well' need a physician? Most assuredly, but who is to convince them when they appear to lack the faculty of conscience?
Excellent explanation.