Keeps the narrative simple and erases the political and existential nature of the struggle by collapsing it down to Evil Mooslems vs The West

If westerns knew there were like twenty groups with different beliefs and politics united in to a literal Rebel Alliance they might ask the wrong questions.

Alternately; The News Media are just dumb as hell propagandists huffing their own farts who don't really give a shit.

Both of these things may be true.