Arguably it's not surprising. America is the largest country with "English" as their primary language and its rot goes further afield to the point that the American version is often seen as the right one. I've friends who in high school correctly chastised their English teachers because their teaching was entirely American English whereas they, being from a mixed English/other family, had been raised with an understanding of English not American English. It apparently was a very awkward parents evening when the English parent met the "English" teacher and proceeded to correct them on an extensive list of errors. Loudly.
Add to that English still being the EU's official language, despite France's renewed efforts to get it back to French, and American news/politics tending to be some of the loudest in the world you've dragged in the Europeans too.
Of course it could be simpler and just be that a majority of the mods/frequent posters are American.