Airbus stands to gain the most from trashing Boeing, Airbus is an international consortium of many countries that fully subsidize their operation. Many of the negative stories, that always manage to get Boeing in the headlines, originate in British tabloid papers.
That’s one reasonable answer.
There may be others.
For example, Red China is trying to break into the airliner business. Wrecking the good reputation of an established manufacturer certainly wouldn’t hurt them.