I would say that he did this for two reasons.
First, I think that any person stranded on an island like he was would want to have something that would be familiar -- that would remind them of home. I would think it would give you some hope if you did that -- you would feel like "I haven't given up on my past -- I'm going to get back to England some day."
Second, Defoe was writing at a time when English people thought they were the greatest people in the world. Their feeling of superiority was one reason they were going out and taking colonies. Defoe would have wanted to portary Crusoe this way as a way of showing that English ways are superior and that people should follow them in order to remain civilized.
In the book "Robinson Crusoe" Crusoe had come from the home country of England at a time when English tradition plays a very important role in a person's psyche. After Crusoe was stranded on the island he prepared for the day that he would leave the island. He continued to need the part of civilization that was not present. Although he was alone practicing the traditions that were familiar to him continued his connection with his homeland. He even made an attempt to escape the island but it was unsuccessful. Crusoe was proud of his role as an Englishman and the ingrained need to continue with traditions gave him comfort and stability in an unfamiliar place.