Ronaldo is a good player, but not for Napoli. Spalletti already has a solid squad, he don't want to spoil it with the presence of Ronaldo who can break the concentration of players.
Napoli players have put in a great game, Spalletti is very satisfied with the performance of his players. Without Ronaldo presence Napoli can dominate the Serie A standings, I think Ronaldo is not in Napoli plans because Spalletti is very satisfied with the squad they have at the moment.
Actually I'm not too sure about things like this but when there is no club that wants to bring Ronaldo and the desperation of wanting to move can actually be another factor for him, but indeed this is a frustrating step because I personally expect him to move to a bigger league others even though things like this are still difficult now.
Actually I quite feel that this is indeed a difficult thing because I don't want to believe he will move again but with the condition he is at Manchester United it is clear that moving is the solution.