Most of that Germany team made their senior debuts after or just before that tournament. The whole point of U21 football is to produce players for the full team. If a player has already been playing for the full national team for 3 years then the function has already been fulfilled, you don't drag them back to play in the place of somebody who's played throughout qualifying (and needs the experience more). Italy could have had Verratti playing the other day but whats the point when he's having the full national team built around him?
Wilshere made his England debut 5 years ago FFS.