The golgi apparatus remains in close association with the endoplasmic reticulum, because
materials packaged by golgi apparatus are transported to the ER
materials to be packaged by golgi body transported to the golgi body from ER
both golgi body and ER have cisternae
both golgi body and ER have ribosomes
Proteins produced in RER are transferred to the golgi apparatus where they are packed to be transferred in the cell or out of the cell.
That's why it is in close association with RER.