That is such a risky move. If he waits till his contract expires, BVB will not be playing him weekly knowing he could leave on a free.
2 years in football is a very long time, loss of form, injuries, never know what can happen. With the riches on offer, there are only a handful clubs that offer those wages.
BVB will probably thinking, will there be clubs in for Sancho next season? Like now, if we are willing to wait one season, next season other clubs will be willing to wait and take him on a free.
I cannot imagine a team next year saying we will spend £120m on sancho when wait a year and he will come on a free. With age on his side, teams can afford to wait another year or two.