If your employer offers you a raise, you usually take it unless you are massively unhappy. Even with the new contracts the level of wages Kane (arguably the top PL striker) earns compared to Rooney (Man Utd 4th choice striker these days) is paltry.
Interestingly, the new contracts don't really deter a player form leaving. If, for example, Levy has offered Kane a bumper deal and it's 125k per week (i have no idea what it actually is), Kane can probably assume he'll stay at that level for a couple of years and it's likely close to the top of what Spurs can pay for the next few years as they sort out the new stadium. If Man City then come in and offer something obscene like 350k per week, he'll have a decision to make.