Thank you for your input. Have your events been sanctioned and if so, how has that impacted the quality of the decks? (both those that T8 and those that do not)
All of our events are non-sanctioned vintage (10 proxy) and I think this plays a big roll in us getting the numbers we get. I've been to sanctioned vintage events in the Netherlands and they tend to get about 20-ish people. With sanctioned events we do tend to have more non-powered / Fish / Aggro decks because of the lack of power.
I think you'll find that has a lot to do with it. Also, professional chess is much bigger in Europe than elsewhere, as are difficult boardgames (Puerto Rico, Risk or Settlers, as opposed to Monopoly or Scrabble, say), which suggests that other professional-ish games like Magic are much more likely to thrive there than in the USA.
Sure this accounts for some part of the whole story..But I do think some of the points I mentioned earlier do account for the success of an event.