Why was the wealthy Parsi merchant Ratanji described as being unhappy despite his immense fortune?

According to Chapter 14, Ratanji was a very religious and popular merchant with vast wealth, property, and a charitable nature. Despite this outward appearance of swimming in an "ocean of joy," he was plagued by an inner worry. His deep sadness stemmed from the fact that he had no son, having had twelve daughters one after another. He felt that his great wealth and happiness were entirely fruitless without a son to continue his lineage, which caused him constant contemplation and unease.