Because you are making an assumption that they did talk to them. Most people avoid confrontation whenever possible(in my experience).

People often need to vent when they are overfrustrated by not being able to resolve a problematic scenario, or are not able to remove themselves from being around the situation that is causing them the stress(like when co workers are being toxic af at each other and keep.dragging you into it and you are stuck working next to it all day because your desk is in the same area etc)