Answer: God, Religious persecution and Interaction with American Indians.
During the colonial era, writing literature about any of the nobility could result in serious consequences, so not many people were bold enough to write about them.
At that time, literature about science was not as popular before the industrial revolution.
Literature about God and religious persecution were common because the different factions of the church were trying to establish their religious superiority over the other.
Also, religion was a key factor to founding most of the colonies. Most of them were founded on the principles of religious liberty. For instance, the New England colonies existed to provide a place for puritans to freely practice their beliefs. However, these puritans didn’t give others freedom to practice other religions. The literature highlighted this.
Texts about interaction with American Indians were common, as well, because the colonialists at that time attracted a good amount of fascination from the locals.