You think selling out a stadium means that they are better fans? It's a small stadium in one of the largest cities in America. The fratboys need something to do over Summer Break, and the executives need off days from the Country Club..
Wrigley isn't small, it's actually pretty typical as far as ballparks in the majors go. Even most of the newer, "bigger" parks with 3 decks and luxury suites hold between 40-45K, and Wrigley's capacity is right around 42K.
If your argument is that Wrigley's dimensions make it a small ballpark, that argument is uqually false, as Wrigley is longer down the lines than any other park in the majors.