Spurs have been for a long while his destination of choice but they clearly hesitated when his hamstring went ping, Chelsea saw a late alternative to Chamberlain once he’d turned them down and made an offer that took Barkley and his agent by surprise and at which point stalled them for whatever reason (probably given the previous year long speculation about Spurs and the planning of the move) hoping they’d be back for him now. In the interim either Chelsea have become more palatable after consideration or Spurs interest has cooled given they could actually continue to wait out the final 6 months and get him for nothing in the summer.
Without his hamstring going he would have definitely been off last summer.
Spurs were never his destination of choice, he would have been taking a pay cut.
It's always been about securing the most money for him. His hamstring going was more of an opportunity for him and Chelsea to make/save some money.