"Why don't you write to me?"
Translation:¿Por qué no me escribes?
When an interrogative like "¿Por qué?" is used in the Spanish it changes up the word order in the Spanish sentence. English changes up the word order in questions also. You are running. Are you running? So I assume "usted" would come after the verb in your example. ¿Por qué no me escribe usted? But use of pronouns is rare unless there is a real need to clarify who you mean (usted, él, ella) or if you what to emphasis one persons does an action instead of another.
Jaja. Why did I know the answer to this, write it out.. last second I second guessed myself and instead stout "me no escribes..." CAN YOU SAY FACE PALM!