To be absolutely honest, I don't think anyone can help. We don't know anything at all about why Shakespeare wrote his plays, as we don't have any first-hand information from Shakespeare, from his patrons, or from his actors, about the circumstances of each of their composition.
All we've got is the plays - and you have to make your own judgement about what each play is trying to do and how successfully it does it.
Best I can do, I think is give you a few pointers about things to think about it in the play:
- The setting of the play in Renaissance Italy points to a fascination that Shakespeare and the Elizabethans seem to have had with Italy as a place of hot-blooded passion, fashionable clothes and attitudes, and young, heady people.
- The play seems to start as a comedy, and only twists into tragedy on Mercutio's (accidental) death. The youthful high-jinks of the first scenes of "Romeo and Juliet" seem closer to "A Midsummer Night's Dream" in youthful high-jinks, rather than the ominousness of a "Macbeth" or a "King Lear". Is Shakespeare trying his hand at a different sort of tragedy?
- The play also relies on fate (their love is "death-mark'd") and chance for it to happen - look at the way Friar John cannot, randomly, deliver Romeo's letter to Mantua, which brings about the dual suicide of the final act. Is one of the objectives of the play perhap to ask the question - why do bad things happen? What is tragedy?