If that's his game then maybe Nuno prefers to play to his strengths rather than doing a poor impression of Saiss or Neves. You never see either of them playing the Alf role, it would be quite a coincidence that he should perefer that kind of midfielder every time and only when Neves or Saiss is unavailable. Like said Dave, I suspect he simply can't help himself. Not to exaggerate their similarities as players, both fulfill a particular niche and one which, in my humble opinion, happens to be quite unsuited to the way we play most of the time - the two holding midfielders are essential for balance and to link up play in between flying wingbacks and wide forwards.