I have a feeling (And I'm in the tech field so it's not like my feeling is uninformed, but I also don't have a lot of data to back this up so sorry about) that because most people who watch YouTube are in the United States ( And because of how populous we are as a country as opposed to a conglomeration of countries. ), the algorithm sort of promotes them a little easier. Whereas people in other countries, Britain included, have to get more popular before they are shown to most of YouTube's audience.

I saw a thing years ago about why PewDiePie was the most subscribed person. Although I think that information's old. I don't think he's number one anymore. But it basically came down to "he moved throughout Europe a lot and then moved to the United States." And because of that, they kept showing his stuff To new audiences based on the region he moved to, but then he kept his subscribers and his subscribers kept seeing his content over time. And once he ended up in the States, he had the biggest new audience of all, and since he already had a lot of subscribers, it just rolled up from there.

Now, to be fair, that was years ago, and the YouTube algorithm has probably changed many times since then. But I still bet that there's some regional bias, and the fact that there is so many people in the United States, and that their content gets pushed so much more regularly, is probably just a product of that regional bias.

Now of course there's like twice as many people in Europe as a whole compared to America, but borders matter to the algorithm. So with all the countries cut up a lot smaller and with states not having the same border rules as countries do, things in the United States just tend to spread faster, quality be damned, I think.

Because YouTube doesn't publish their algorithm in any way, we will probably never know the real reason. But this is as close as I can get based on what I've heard about previous algorithm practices.