First of all, please note that there was not just one policy change during this time. Instead, there were a few different changes. The general trend in the changes was towards more English control over the colonies, but this went in fits and starts. So far as we know, the changes were driven mainly by changes in political leadership in England and by England’s general desire to get richer and more powerful.
The general trend was caused by the idea of mercantilism. The English felt that they had to have greater control over colonial trade. This was because the theory of mercantilism said that a country became rich by exporting more than it imported. The English wanted to exert more control over the colonies so they could control what the colonies imported and exported and who they traded with. This would, it was believed, make England richer.
However, the details of the changes were affected to a great extent by changes in political leadership. The changes began when Oliver Cromwell took power in England. Then, for example, there was a major change in 1685 when James II came to the throne. He tried to exert a great deal of control over the colonies. This trend was reversed when the Glorious Revolution removed James from power. The new rulers, William and Mary and the Parliament, tried to bring more coherence to colonial policy and make it more organized.
In short, then, the overall trend was driven by mercantilism while details of the changes were caused by changes in political leadership.