Talking about 'culture' in general is a crapshoot but here goes:
Something also to consider is what has changed in general since 2006 in the ways people consume media and spend their free time?
HDTVs and online streaming of games have heightened the quality and accessibility of sporting content at home. Spend thousands of dollars on tickets, concessions, and parking or a couple hundred (at most) a year on a nice TV and beer and food at home? No commute to the park, no problem.
Along those lines, if it's a Friday night and you don't want to sit home, go watch the game at bar with 100 HDTVs, cheap drinks, and an atmosphere in which you can easily communicate with you're friends instead of shouting over the PA and the drunk jamook behind you.
Gas was 1$ cheaper per gallon in 2006, and people LOVE to complain about gas prices and use it as an excuse for not driving places.
Why spend 200$ on a Sox game when you could go on Groupon or Living Social and do an outdoor activity for a fraction of the price?
Totally anecdotal, but it seems like there are alot more street festivals/concerts/ethnic fests then I can recall there being.
The Blackhawks won the Cup, superceding the Sox as the city's most recent champion, thus taking attention and money away.
I don't think any one of these things had a huge impact, but collectively there may be an effect.