Why doesn't Romeo know Friar Lawrence's plan?

Balthasar wanted to be free from Romeo's service, so he lied and told him Juliet was dead.
Friar John was supposed to deliver the message, but got quarantined.
The Apothecary wants to make sure he's not arrested so he holds on to the letter.
Friar Lawrence forgot to tell Balthasar.

Romeo doesn't know Friar Lawrence's plan because there were several unforeseen circumstances that prevented the message from reaching him. Balthasar, Romeo's servant, wanted to be freed from his service, so he lied to Romeo and told him that Juliet was dead. This misinformation kept Romeo from being aware of Friar Lawrence's plan. Additionally, Friar John, who was supposed to deliver the message to Romeo, got quarantined, further preventing him from conveying the plan to Romeo. Furthermore, the apothecary, who was responsible for delivering the letter to Romeo, wanted to ensure he wouldn't be arrested, so he held onto the letter instead. Lastly, it seems that Friar Lawrence forgot to inform Balthasar about the plan, which ultimately led to Romeo's ignorance of the situation.