Because they've got 11million registered fans in the world might be something to do with it.
People who know football would know that Juve are by far and away the best supported club in Italy yet paradoxically they get poor home crowds. This is because Turin is one of only 2 cities in the whole of Italy where Juve AREN'T the best supported club. Juve have more fans in Milan than both Milan and Inter, bet you didnt know that eh? They get huge crowds for away games with their fans often outnumbering home fans and there has actually been a big movement to try and get them to relocate to another city, hence the decision to play UEFA cup games in Milan during previous seasons (when they got 80,000+ sell outs every time).
The new stadium is all part of a move to actually try and engage with the population of Turin and return to times of only a decade ago when they averaged over 55,000 for home games.