I completely agree with you here btw, Hickey was the first of the Scottish contingent (aside from Liam Henderson) to make the move, and according to tranfser market, he went the same summer as Turnbull went to Celtic. After the success of Hickey, any half decent youngster was linked with a move to Italy, Josh Campbell was even touted at one point.
I don't recall Turnbull having any European suitors, could be wrong here btw.
Italian teams seemed happy taking young Scottish players, is it possible Turnbull just missed out on that, I reckon Italy would be perfect for his style of play.
Again, I could be wrong, the only two teams that put in sensible offers for him were Norwich and Celtic.