Because luck was exactly what Inter lacked last year.
For me last year Inter was not unlucky but the schedule of matches in various competitions put heavier pressure. If last season Napoli also had a schedule at UCL and several other competitions, surely Inter were still able to win the Scudetto last season. Inter get 79 and Napoli only have 59 scores in one season. This difference proves that Inter is still a very good team last year.