Because more often than not, he has always preferred a 4231. Also, apart from City, who are a highly possession based side, what other teams have played like that with success? Its risky and even Pep has had to change his ways in recent years.The way I see it, Ole doesnt trust A) his CB's to play with a single CDM, or B) either of Fred or Mctominay to fulfil that role on their own. With new personnel why wouldn't he change things?
City have player with the likes of D.Silva and KDB in front of an actual CDM for years - can we not do this? Going off topic slightly but we need more creativity when Pogba goes.