For me, the interest dwindled to the point where I really didn't care to go the games anymore. My step-dad had season tickets (from a friend of his) for the Spitfires from the mid 1980's until the mid-90s, when he got switched to afternoons, so I got a pair of tickets with a buddy, which transfer to getting season tickets with my father and his wife, as well as my wife and daughter. We kept our seats until 2010-2011 season finished (and sold half of those from that final season). The prices were getting too high, Thursday nights where a rush home, eat, rush to arena (5-10 min drive), spend money on drinks/snacks/etc. I think after the back to back Mem Cup seasons for the Spitfires, I had WFCU overload. My kid played hockey there, and I coached her (every Sat/Sun), Spits on Thurs (plus whenever else they had a home game), plus I played there weekly - so that is minimum 4 of out 7 days at the same arena, plus with the long playoff runs. It became a chore almost. Wife started working afternoon, kid got older and didn't care, so then it was just me (and my Dad and his wife), and I just had enough. Surprisingly, I didn't/don't miss it. I have been to 3 games since I gave up my tickets (all for free for whatever reasons).
I think I agree with a lot of what is said on here already - the rivalry thing was huge - what topped a Windsor - Plymouth or Windsor - London game!!!!! I am fine with the game evolving (less fighting, less big hits), and fans have to expect that. These game sure aren't the same, but neither are they at the NHL level. Mind you.....I was never a go to a hockey game for the fights type of fan. It was more about a great product at a great price.
For Windsor - is it that fans expecting a winner every year (I hope not - Windsor fans should know better)? Cost is a big factor. So it parking at the WFCU Centre - not nearly enough parking for a 6600 seat arena, and 3 community rinks.
For other cities - I am sure the same factors apply everywhere. Population size too. Also demographics have to play a part - thus the lack of success in places like Brampton, Mississauga? Population/demographics tie in with each other - some places have lots of better entertainment options, and not everyone is a fan of hockey.
Heck...around the 2000-2001-2002 seasons, I was doing fan bus trips, etc. Do teams even really do this much now? That was some great fun times! Nothing like being on a coach bus on the way to watch the Spitfires on a highway from Brampton to Owen Sound and getting turned around because of a blizzard!