So your point is: What is the sense of only getting 50-60 Million next year and having Sancho for one more season given the fact that BVB never ever wins the title even with Sancho? Iam understanding you right? That sort of thinking would undermine every effort (or claim) you got as a footballclub.
Everything can happen, and there is also a thing called Champions League. Do i really have to argue that its always the best to get the best team possible?
The point is: They highly probably want to sell, but only for a demanded price and in a specific timespan. And if not, they switch to plan B, and won't shed a tear cause they have the burden to have a Sancho on board for one more season. A comparable situation for the situation next season might be Pulisic. They got 60 Million for him, he had got only 1 year left, and played a minor role in that season, Sancho is by far better than him and is english. Corona situation could also be a little bit more back to normal, and another clubs could be in for him. So they might not stress themselfs and say "if someone pays the 120 Million now, great, if not, we get 50 or 60 Million or more next year, thats also fine and we will get these 50-60 Million at least for sure". They already proofed that if some offer don't fit their needs they carry on. Lewandowski comes in mind.
They are one of the financially most healthiest club, they aren't desperate for money. They will just stick to their plans. At this state negotiations might to be at a point where United and BVB are discussing the exactly conditions of the transfer, but if the all-over-sum don't is as much as the BVB want (or it really takes too long and cuts into their season planing), they will just wait till next season.