Matri was in his 'best' years and already a developed player. What you're saying is basically having a 22yo player as our 3rd of 4th option out there. Not only that he wouldn't score 15 goals, but there's no way he'd be developed the same way he's right now at Torino. What he needed and still needs is a lot of playing time in order to become better -- which is not something Juventus can offer him at this point. Not having here makes sense and it was a right thing to do.
let me give you an example.
Dortmund in the 10/11 season like lucas barrios as their main striker which scored 16 goals and 6 assist. As a backup their had 22 year old Lewadolski which scored 8 goals that season. the following season lewadolski aged 23 had adjusted properly, he scored 20 goals. Dortmund clearly saw that he had potential to become a good striker and considering that lewadolski scored 14 goals in the polish league (which is weaker than serie B).
Juve could have followed the same pattern. immobile clearly showed some potential scoring 28 goals at the same age as lewadolski scored 14 in the polish league. However we decided to play him in a disorganised and very uncreative team like Genoa so immobile had very little chances and turned out to only score 5 goals. Now that he is at torino which is a a very organised and creative team thanks to cerci, he is scoring tonnes of goals.
The environment where the player is determines his performance, if the players around him play well he will play well. That's why I say that players iturbe are ready to join our team because they are able to step up their game from the promising performances at their current clubs.