Juve are doing it to win the CL, to be the best you have to buy the best and the guy is clearly that, goals galore at every level and in every league he plays in. Expect he'll score a shedload more for Real and further prove rather than staying in the comfort zone.
Credit to him, could have stayed at Real where he's already a legend, but instead he chooses to move on and try to prove himself elsewhere, that's what stands him apart from the others.