The only answer that can be given is that for some reason the two families were feuding. Their houses were joined under one roof, probably with a courtyard in the middle, and their mutual hatred was so great that they built a wall to avoid having to even look at one another.
The story of the star-crossed lovers Pyramus and Thisbe has influenced other writers, particularly William Shakespeare. In A Midsummer Night's Dream, Bottom and his group are preparing a play about the lovers: "The most lamentable comedy and most
cruel death of Pyramus and Thisbe" (Act 1, scene 2). Likewise, the theme of Romeo and Juliet is basically a retelling of the story.