Juventus halted Sancho transfer because they just signed Francisco Conceicao, and they don't have enough funds to sign Sancho. They're planning on selling one of their winger in order for them to raise funds for the signing of Sancho. If Juventus did not succeed on selling either Nico Gonzalez or Timothy Weah, they might not be able to bring Sancho in. No club wants to add more players to their squad without selling to replace.
That's part of the move Juventus must make, but if it doesn't work out for Juventus, Sancho might be a little hesitant if other teams don't consider him in his current situation. And I completely understand Juventus' decision, as Juventus' financial situation is limited, so selling existing players to bring in new ones is a common solution for every team. I only hope Sancho can move to another team from Manchester United if he is truly no longer needed by Manchester United next season.