Why did the Middle Colonies have such a diverse European population?

The Middle Colonies refers to Delaware, New Jersey, Pennsylvania, and New York. These were established after the Virginia Colony had become a plantation powerhouse in the world economy, and after New England had established Boston as a trading capital. The goal of the British government was to quickly populate the area in between Virginia and New England in order to protect their claim to their North American colonies.

Beginning in the late 1600's, Britain granted charters to lords who were willing to set up colonies. Unlike Jamestown, that was set up to maximize profit, and New England, which was set up by religious separatists, the Middle Colonies just needed people.

To do this, the colonies adopted religious "freedom" (usually meaning any Christian denomination could be citizens). This allowed for various Scot, Irish, Dutch, and German settlers to establish farms. The colonies also adopted a "headright" system, which meant that land was given to each male settler that came over, and extra land was given if they brought servants.