You're just blatantly disregarding facts here.
2011-12 10 goals - 68 shots attempted. 1 goal every 6.8 shots attempted. He also had 3 legitimate goals disallowed that season. Against Milan, Napoli, Parma. Which would have put him at 13 goals - 71 shots, 1 goal every 5.4 shots.
2012-13 was even better with 10 goals from 48 shots attempted or 1 goal every 4.8 shots attempted.
In his two full seasons here, his chance conversion rate was actually quite decent.
Quags for example on the other hand:
2011-12: 49 shots - 4 goals. 1 goal every 12.25 shots
2012-13: 88 shots - 13 goals. 1 goal every 6.8 shots
Another example. Amazing Tevez this year, who is very amazing:
133 shots - 20 goals or 1 goal every 6.5 shots
Are you going to trash Tevez for having a bad conversion rate too?
Matri, during his time at Juventus, was very decent at converting chances, this was one of his best features. You are mistaking Matri missing occasional ridiculously easy chances, for missing a lot of chances. He has a tendency to fuck up the easiest of chances, but his actual chance conversion rate was very good for his entire time here.
So now, that I've proved you very wrong, please apologize. Thank you.