At first it seems ridiculous that almost everyone in Hell should be not just Italian, but Florentine. But Dante is not just settling old scores. He damns even those who never harmed him, who on the contrary were good to him, merely because who or what they were offends him.
Some people can’t endure being indebted to others. This may be why Dante condemns Brunetto Latini, his guardian and teacher, to Hell. Of course it’s not Dante, but god, who condemns these sinners. Dante pities them. Hate the sin but love the sinner is the alibi with which the faux religious justify their sadism.
Sadism is so common that it’s easily overlooked, especially when expressed in beautiful terza rima.