You can't block players from transferring... none of the good players would ever come. You either have a policy that you will accommodate players when they ask to leave OR players will demand an exit clause. In Juve's case, they have the policy likely because they feel that they can get better pricing than an exit clause.
Real Madrid, Barca, etc. all have similar policies. Exit clauses are mandatory but they put stupid amounts there like 1 billion lol. In the end, they allow a player to leave if he asks to.
Bayern and PSG are the only two clubs that actively block players. PSG does this by giving its players huge wages in exchange for waiving this right. Bayern does it by targeting German, Bundi, young up-and-coming players or late prime ones who aren't worried about the next move. You rarely see a very high level young player that has other options move to Bayern unless he's German or in Bundi already. Robben, Vidal and Alonso are the ones I remember that were outside Bayern's typical recruiting circles.. Robben went there because it was, by far, his best option after all the injuries. Vidal's best offer was also Bayern and you had Pep to lure him. Alonso was going into his last contract anyhow so he wasn't looking past Bayern.... and again, there was Pep.
So i don't think Juve have much of a choice. It's a profession. Players want to get paid. Juve can only keep its super elite talents if it can pay the required compensation.