I think this is for a few reasons; America is a [the?] global hegemon; so American domestic politics have some earnest global relevance. But more than that; reporting one country's news is more efficient than reporting N countries' news. Fewer stories means fewer writers to pay, less research and investigation to do, etc. Furthermore people have an appetite for news, but a finite appetite; sate people with news about America and you'll have them thinking less about local issues. Therefore, news organizations in other countries have both an economic and political incentive to report American news instead of local news. What's more, America encourages this because for America it is a form of soft power to live rent-free in the minds of everybody else.
Point is: when a narrative becomes taboo in American media, that's likely to rub off on the rest of the world. Particularly so in countries where a sizeable portion of the population consume at least some English-language media, participate on English-language forums, etc.