Tottenham could sell Kane at a higher price this season. And with that money, they can stabilize the team, by purchasing new players. I think it's better to build a stable team without relying on Harry Kane alone. If Kane is not sold, they will lose the opportunity to make a lot of money.
They could also do the same with Son as well, basically what Dortmund is going through at the same time. Dortmund had sancho+haaland and now they just have haaland and looking to not sell him for a small price, they were "offered" unofficially 150 million but they wanted something like 174 million I think. However, Son+Kane could bring in as much as 200 million which would be insane for Spurs, they could get like 5 players who are worth 40 million, that is going to be just surreal for them and would make that team into a contender nearly in one single off-season.
However, most of the time real life is not like football manager where you can just sell anyone the moment you want and get anyone with just one offer, it takes a lot longer than that and I feel like it is not going to be easy for them to do such huge moves that quickly, which is why they are avoiding it as much as they can.