It looks like Spalletti left not because Napoli failed to defend him, but in fact Spalletti himself chose to rest. Also about Osimhen, rejecting offers from other clubs can also be the wrong choice. Because after all, if later Napoli doesn't get performance and doesn't get good results, then maintaining Osimhen will be useless. But indeed, defending Osimhen, of course, Napoli hopes that Osimhen can make good results for Napoli, such as defending the title. But, if Osimhen is sold at a high price, then at least Napoli can still get other quality players. So yes, retaining players is basically not always the best option, because of course there will be many repercussions that will occur from time to time.
Spalletti reportedly had an argument with the club's owners, no further news regarding this news and its truth. What is clear is that he wants to rest and will not coach any club for a period of one year. A wise decision put forward by Spalletti that during his time coaching Napoli most of his time was spent thinking about the club, after winning the Scudetto it was the right time to rest.
The impact of Spalletti departure could be enormous, because he has built a squad for three seasons. instead Rudi Garcia has a big task to defend the Scudetto title next season, currently keeping his star players from leaving is the top priority.