If AC Milan win, they will take over the first position in Serie A from Inter Milan. It is a great motivation for them to play very ambitiously and aggressively.
Napoli's performances are now the most erratic among the first-tier teams in Serie A. They were very strong at the start of the season. They won a number of matches in a row and were at the top of the points table. But now they are not playing well. They have lost two of the last five matches and drawn one. Not that he has lost to any of his strongest teams. They lost against a relatively weak team. So now it is relatively less risky to bet on the victory of AC Milan than to bet on the victory of Napoli. Because AC Milan's performance is good, at the same time their opponents are weak.