Starting first, money, and money, as well as money.
But seriously, how are we measuring dominance, because in the US I never see a Japanese website, but, we're not typing in Japanese, search engines aren't showing us results from other languages. However, their internet is rich in presence and culture, they're doing their own thing.
I'd wager, most nations with widespread internet have a thriving internet culture and common websites you've never heard of.
Ireland is a "western country" but most accounts. But the reason you don't notice the Irish is for a couple reasons. Ireland has a population of a bit over 5mil. Canada about 7 times greater and the US, roughly 66 times that.
Secondly, they all write in English on the Internet and people aren't running around shouting about what countries they're from. So you probably make assumptions where everyone is.
Unrelated, but my Lemmy client says this post is a year old. Is that right? It appears in my feed as if it's recent, and other recent comments suggest they're seeing it in their feed too.