Maybe Juventus were hoping that they could take these players and turn them into higher level players at their club. But if they were unstable players from the start, then they basically stayed the same. Now Juventus want to sell Vlahovic and Luis, but since they failed to prove themselves properly at Juventus, it is clear that it is difficult for them to get the price they want for them. And with Vlahovic, they have already been trying to sell him for the second transfer window in a row, so I think in this case it would be better to lower the price and replace him.
Their thinking was completely right and they wanted to strengthen themselves and take themselves to a certain point and in the same way they could have made some changes in their team. It is not that Juventus is not such a capable team that every player of theirs plays better and better, some of them are such players who really should have been changed. If that is the case, I do not find this decision of Juventus bad because when these players leave, they can replace them with some better players who can improve Juventus' performance. Obviously, when they are not able to become successful players in their own team, other teams are also forced to think how well they will be able to play in our team. If they really do not want this player, then you are absolutely right and they should do the same.