Lucas, similarly to Kuyt, were changed by Rafa after they signed. We've seen how Kuyt has proved himself especially towards the end of the season by netting a fair amount of goals for us, this is all about giving him the freedom to play where he wants to play. Lucas clearly isn't a defensive midfielder and so keeping him there is pointless + on the rare occasions when Lucas has bombed forward, he's shown creative spark and isn't afraid to shoot.