More than a year ago, the league warned GMs that it was unhappy with the number of long-term deals whose cap hit was made more manageable by heavily front-loading the contract and tacking on years at the end. These deals worked for players because they made most of the money early in the contract; the deals worked for GMs who were looking to keep the average cap hit as low as possible, giving them more financial flexibility....
Presumably, the NHL found no evidence of an agent or player giving a team the old "wink, wink, nudge, nudge" about not playing after a certain point in the contract since the team wouldn't be on the hook for the rest of the deal (provided the player wasn't 35 when the contract took effect, as was the case with the contract extension Pronger signed with Philadelphia).
Clearly, though, the league believed its warning to cease and desist these kinds of deals was falling on deaf ears; and when it saw the whopper deal Kovalchuk, his agent Jay Grossman, and New Jersey president and GM Lou Lamoriello came up with, the league said "enough."