Aside from the fact that Wrigley is truly a lay cathedral, and one of the most storied and cozy places to see a game, any sport, the fact that their games were broadcast on WGN has to be a factor.
I grew up in rural northern Michigan, but the Cubbies were televised and picked up on cable. That was back when hardly any baseball was televised. You could see the Tigers on opening day, Costas called the game of the week on Saturdays, there was the All-Star games and the playoffs, but that was it. So you had Harry Carey broadcasting day games, which hit right about when I got home from school. It was perfect. My family went to games when we were in Chicago. I was a Cubs fan (as well as a Tigers fan) until I was old enough to know better.
FWIW, back when I went to games, I remember being amazed at how knowledgeable and friendly the fans were. They knew the opposing players, there was generally a lot of conversation between fans. Tiger fans were more reserved.