It's all about leverage -- in business, in sports, in life. Or, at the risk of dating myself, it's all about "hand," in the Seinfeldian sense.
When it comes to Harry Kane and a move away from Tottenham Hotspur, he simply has very little. Which is not to say he won't move this summer -- transfer markets can be weirdly unpredictable and subject to knock-on effects -- but rather that unless there's a sudden bout of irrationality, it's unlikely.
There's a school of thought that his time at Tottenham has come to an end, fuelled by briefings from his entourage, Kane himself saying that while individual awards are great, he wants to win silverware ("and that's not happening right now") and the widespread reports that Spurs are ready to deal.