7 points of advantage at a distance of 63 points is more than 10%. Juventus will not be able to win endlessly, they will also lose points (like Napoli, like Milan and other clubs), so these 7 points are almost a guarantee of the title. Moreover, with each game this advantage will increase - as you understand, 7 points of advantage at a distance of, say, 9 points (three games) is much more significant than at a distance of 21 games.
They might losing points only on a draw and winning it the rest , while napoli could slipped losing a lot of points under juventus pressure.