Read this line from the prologue of Romeo and Juliet.
A pair of star-cross’d lovers take their life;
What is the most likely reason the prologue reveals this detail about the play?
to engage the audience in the tragic story
to warn the audience about the bloodshed
to raise audience sympathy for the parents
to build suspense about how the story ends
I think the answer is 'to engage the audience in the tragic story'. I would only reveal the end to capture the attention of the audince and make them wonder why/how the story ends the way it does.