That axing was fairly well-documented and one of the few cases where we know for sure that it was cancelled and why. It was a school that was pissed, not the yakuza. One of Miyashita's assistants accidentally snuck in the name of a real school in the list of schools the villain had taken over, and that school complained to Shueisha for being associated with the series, so Shueisha held Miyashita responsible for not supervising his assistants enough.
As for this, though, political satire is well protected in Japan's constitution under freedom of expression. And don't forget that pretty much nobody liked Mori. Miyashita's got big balls, but this isn't why.