@bobbyvictory and Pittsburgh, PA is physically closer to Columbus, Ohio than it is to Philadelphia, PA. I feel like you're cherry-picking your data points here.
2008 (Indianapolis) - "over 100 players"
2009 (Indianapolis) -
2010 (US Nats ?? ) - 117 players
2011 (??) - ??
2012 (??) - 186 players
2013 (Philadelphia) - 232 players
2014 (Philadelphia) - 341 players
2015 (Philadelphia) - 460 players
2016 (Columbus) - 350 players
2017 (Pittsburgh) - 429 players
I can't find numbers for years prior, but I remember them being around 100 from back to 2003.
When looking at all the numbers together, I could use this very same data to argue something like ...
Vintage was largely stagnant until 2010 when Lodestone Golem was printed, after which it exploded in popularity. In 2016 Lodestone was restricted and attendance dropped massively. Over the next year workshops began to get good again, and so attendance went up. If we had some way of mapping "how good shops is in the meta" vs "champs attendance" I bet you'd see a similar curve.
Of course, I don't think there's a causal relationship there at all ... I just think humans are really good at looking at data and finding a narrative that fits the opinion they had before they started looking at it.