FOX was the best TV partner the NHL ever had. Ratings were through the roof and FOX treated the NHL as a major brand. They should have stayed with FOX, but they burned that bridge (maybe forever).
NHL got greedy and left for ABC/ESPN, where they were treated like absolute dog crap. Didn't help that the league entered the dead-puck era at the same time. Ratings nose-dived, ESPN mocked the NHL nightly on SportsCenter, and the league's image was flushed down the toilet.
ABC/ESPN left the NHL for dead in 2004. Refused to offer any guaranteed money - only a revenue-sharing deal. One of the major reasons there was a lost season in 2004. The league had nothing to lose. They hit rock bottom and were willing to waste a season to get a better CBA.