A content warning advises "This story about the Rwandan Civil War contains scenes of graphic genocide". The content warning speaks to a variety of readers, whether they are an actual survivor of the Rwandan conflict, or simply don't care to read about it. Because really, lots of people are averse to violent content, but rarely does the gravity of that aversion rise to the level of a defined psychiatric disorder implied by the word "trigger."
Furthermore, the particular themes which are listed most often as potential "triggers" are the product, to large extent, of a social construct about what we ought to accept as a valid source of anxiety. A quick internet search turns up hundreds of specific phobias likely to trigger a panic attack in affected individuals. So why do we never read "This story about the circus contains graphic depictions of clowns"?
Somebody reading this right now probably thinks I'm an insensitive lout who doesn't care about combat veterans or suffering victims of past abuse. But believe me, I understand panic disorders and have my own peculiar sensitivities (not clowns...I love clowns) that don't ever show up in anyone else's trigger lists. Can't we just stick with content warnings?