speaking of, there seemed to be a reason behind it -
dias hasn't won enough aerial duals this season, and pep thought stones and laporte were more equipped for that job vs lukaku and chelsea's playstyle, which proved a great decision as they both won 100% of their aerial duals.
Not just that, it was also to counter Chelsea's press (as one would have expected them to have a go lol) and there's no better centre back pairing equipped to beat the press and break the lines. Dias is a more traditional choice but he cannot help us much in the build up.