General interest just plummeted which resulted in news media and networks dropping coverage. This was a time when NHL was broadcast national on Fox - which helped to drive popularity even though non-playoff ratings were poor. Honestly it was probably worse after the 04-05 lockout since during that time we missing over 1000 games.
It's hard to see outside of my Michigan bubble because hockey is a big deal here. Interest has grown amounts my friends dramatically over the past few years. I personally watch a lot of hockey and hit up an OHL game at least once a month.
I just began watching it over the last few seasons and it is now my number 1 sport over the NFL. I love it! It does seem to be getting more popular with tv viewers and now they have special programs on nbc sports network other than the games and they have a show coming to HBO I believe this week or next week. And more and more American players are getting into the league each season which helps its growth I believe. I wish I could live up north just to have the beauty of being in a hockey town.
I noticed those specific markets have dedicated and large fan bases. Detroit, we seen how large Chicago's fan base is from last seasons stanley cup and the parade afterwards. Southern california has a dedicated market, I heard Minnesota is a hockey town too.