Thanks for the explanation :) Yes I think there's a big part of that playing, the exitement most of you have combined with sharing more makes the post more boosted up.
Of course language could be a player too, english is the main language between 28 countries, but that auto-includes american posts.
There's verious reasons, but in the end it looks like they purpously select all US posts for european timelines, while instead it should fairly select european posts.