If there is a clause, is because he and his agent enforced it and we succumbed. it seems we are not in a position to simply say "clause? no fuking way, you are juvebound", at least not yet.
Because if you are going to play tough, to play the game, you need to be able to back it up. Other teams do this by simply offering absurd money and showing great power, above what the player can show. We cant do this because we would need to unleash crazy amounts of money ala madrid or Barcelona in order to shut the players and agents mouth. Since we cannot do that, we need to settle to this kind of clauses in case the player receives an interesting offer from said clubs.
Top of the line players are very well aware that Juventus, while being as great as it is, it has a ceiling...and teams like madrid and Barcelona seem to have no ceiling in terms of glamour, exposure and silverware. Think about it, in a team like madrid, you can not only get famous and rich as hell, but also win silverware.