That could be his nature and the type of person he is. Different people have varied reactions to different things. Others may not take it as an offence, but he does, thus they needed to apologise to him. A squad experiencing bad performance does not need to be divided at this moment in time when they have a number of key matches ahead of them, and this should not even be with one of the team's main players. This may be an example from when Messi was still at Barcelona; you can't have a problem with Messi when you need to win a key match. It is time for Napoli to unite and tackle the challenge and not having personal issues between themselves because of some videos acclaimed to be a jokingly one.
He probably just doesn't accept apologies because he's probably already tried talking to him. I think sooner or later he will stop taking offence, especially the team still needs him on the pitch. Yesterday they won their first match in the Champions League, they started well. Osimhen himself was substituted, by the way.