Carra would be at best cover for Rio or Terry, like he was before. Would there be any assurance he wouldn't be left out in favour of Upson, Lescott or the next CB people are talking about? It isn't he doesn't want to play for his country, he was just fed up with their use of him - or not using him. It's England's loss, he has been a top English CB for years and johnny come lately was preferred to him every time.
He's better off out of it anyway, more chance of winning trophies with Liverpool and likely to prolong his career without the extra games.