The price benchmark applied by Napoli for this striker which exceeds the market price seems to be one of the reluctances of big clubs to make offers to him, so choosing another alternative is done, maybe if Napoli lowers the price of this player then big clubs will start to aggressively provide offer.
Napoli knows that Osimhen is their best player and they don't want to lose him at cheap price. They also really know that they will not be able to keep Osimhen in their club too long. He will not expand his contract with them because with Napoli, they will not be able to win Scudetto too often and play well in Champions League like in the past season which is an abnormal season for them.
So Napoli know they will have to sell Osimhen and the task for them is selling the striker with as highest price as possible.
Of course his presence will be needed by Napoli to defend the title because it was proven when he didn't play when he was injured, Napoli had difficulty scoring goals, maybe that's why Napoli set a high price so when there are clubs who are willing with the amount offered they have the ability to financially find a replacement which is no less good.
Even with Osimhen and Kravatskhelia in a new season, Napoli will very difficult to defend their title. Kim Min-Jae already left their club and again even with same players, the task to defend Scudetto is not easy.