My guess is they were trained on other text from other contexts (e.g. ones where people actually use emojis naturally) and it transferred into the PR context, somehow.
Or someone made a call that emoji-infested text is "friendlier" and tuned the model to be "friendlier."
Maybe the humans in the loop were all MBAs who believe documents and powerpoint slides look more professional when you use graphical bullet points.
(I once got that feedback from someone in management when writing a proposal...)