As far as I know, last season Osimhen had a very large transfer market value which made many clubs unable to get him. Napoli also won't let other clubs get it easily. Because of that, they set a high price clause for Osimhen. This season Napoli's performance has been very bad. Osimhen managed to score 15 goals and was among the top scorers but was unable to provide a good performance for Napoli.
A good player will not be able to provide good performance for the team if he can only work alone without any help from his own teammates on the team. So it would not be enough to say that Osimhen is a bad player because he does not get more good support from his teammates who may still be less able to provide the best passes to him when in the match. Because in fact he still has to be considered a good player at Napoli so that Napoli sets a high price for him so that other teams cannot reach him more easily.