Who knows. My gut feeling is that Pogba was indecisive and the Higuain buy out expiry was approaching so we gave him an ultimatum and he refused to commit so Marotta will interpret that as his wanting to leave.
If a player does not represent a meaningful upgrade, why not stick with players you know and who are already accustomed with their teammates and environment. Change for change's sake is dangerous.
Also, quality CMs don't grow on trees. None of the available ones out there do not scream quality and the ones that may fit the profile either don't want to leave, or the clubs have whacked really high transfer fees on them that we deem as too expensive for their worth. Even people on this forum are not happy about names such as Brozovic, Witsel, Matuidi, Gustavo etc. Why should we overpay for average players? Even if I was in Marotta's shoes right now, I would struggle to see who I would actually go for at the moment.