[lo_zamoyski]

I think the short answer is that the US is the dominant soft global empire (which is to say this is not merely military, but also economic and cultural). What happens in Rome ripples outward into the broader realm.

But I also believe that another contributing factor is that Americans, regardless of political affiliation, often demonstrate a presumption that their own provincial squabbles, concerns, and anxieties are shared by everyone else on the planet. This is not categorically unique to Americans, but such presumption is reinforced by boorish imperial egocentrism.

And, of course, some people simply don't have the sense, consideration, and social grace to know what the appropriate time, place, and means are for expressing political convictions, and as a result, obsessively pollute all manner of social interaction with the aforementioned topics.