The most likely reason that the prologue reveals the above detail about the play is: to engage the audience in the tragic story The prologue of the play “Romeo and Juliet” tells the audience about the place where the play will revolve on. The feud between the Montagues and the Capulets is also been introduced to the audience. The love between the two who belong to these families is also told in the prologue. It is also being told to the audience that if ever the two families would unite together, their unity will be the result of the death of the lovers.
This happens quite a lot in verbs e.g run to running. It is because you double the last consonant in a one-syllable noun for it to become a verb. (Keep in mind there are exceptions to this rule.)
