I'm sure that Napoli lost this game on purpose. They are not in the best position in the Serie A standings and they need to keep playing in the Champions League. The Italian Cup is not important for them and they will not waste strength on it. The main thing for them is to improve their position in Serie A and try their luck in the Champions League.
If Napoli is still trying to improve its position in the Serie A standings, of course Napoli must always consider winning and it would be very unreasonable if Napoli deliberately lost the Coppa Italia to a team lower than them. Apart from that, Napoli also cannot give an excuse if they deliberately lost just because they are still in the Champions League this season, because their fans will certainly be very disappointed if Napoli admits that they deliberately lost a certain match even though it was outside of the Champions League competition.
The Napoli fans will be disappointed, but the team will not go far in the champion league this season; in fact, given their strong opponents, they may even finish in the run-16. We also need to consider how Napoli has performed thus far; under their previous coach, the team's performance was subpar from the beginning, and now that they have a new one, I believe Napoli is going to perform well. Based on their recent performance, which has been consistent since last week, it appears that they can perform better in the serie A league, but it will be difficult for them to advance farther than they did in the champion league last season.
Even though Napoli is losing in the Copa Italian round of 16, and their opponents are simply teams that are not predicted to win, I don't think it is appropriate to label Napoli as weak or as such because there are plenty of teams that are inferior to them. I believe that the best thing Napoli can do right now is to trade in some of their players and acquire new ones.