Why does Inferno have one more canto than Purgatorio and Paradiso?

The Divine Comedy by Dante consists of 100 cantos in total, divided into three sections: Inferno, Purgatorio, and Paradiso. While each of these three sections contains 33 cantos, the Inferno includes one additional canto that serves as a prologue to the entire work.12

This structure reflects the poet's emphasis on the divine number of three, which is woven throughout the poem's design, including its terza rima rhyme scheme composed of three-line stanzas (tercets).1