Inter odds are bigger than Napoli in this match. Maybe the home effects might be considered, yet Napoli should not be underestimated imo.
It is a match at Giuseppe Meazza stadium, a home stadium of Inter. I guess the odds is taken from the home stadium effect.
Maybe because Internazionale is often to Scudetto which makes the odds is bigger, but still people still have sure Napoli will not have a problem in san Siro. Because on paper, Napoli seems to look good as a material player, and with performance, I do not doubt choosing Napoli even draw is a bigger chance for this time. And, Napoli also hasn't pressure about points, because different points is far enough if they lost or draw.
Inter Milan have better tradition than Napoli. Much better as they are a second successful club in Serie A, only after Juventus at 1st position and AC Milan are at 3rd position.
Wiki about Serie A gives us good images on top clubs in Serie A. You would be surprise to see these details, Napoli are a fourth club that have most runner-ups in Serie A history after Juventus (21), Inter Milan and AC Milan (16) and AS Roma (14). Napoli have played 77 seasons in Serie A.
Total seasons play in Serie A
91 seasons: Inter Milan
90 seasons: Juventus, Roma
89 seasons: AC Milan
85 seasons: Fiorentina
80 seasons: Lazio
79 seasons: Torino
77 seasons: Napoli
Total champions and runner-ups
Juventus 36 21
Inter Milan 19 16
AC Milan 19 16
Napoli 2 8