Britain changed its policies because of the impact of the Seven Years' War, which was known in America as the French and Indian War. After this war, Britain needed more help from the colonies to help defray the costs of the war and of the new demands that winning the war put on British finances.
Before the war, the British had pursued a policy of "salutary neglect" towards the colonies. They didn't tax the colonies much and they didn't enforce laws like the Navigation Acts very strongly.
After the war, the British needed more revenue from the colonies to pay for military costs. Therefore, they started to impose new taxes like the Stamp Tax. They also started to enforce laws more strictly so that Americans could not evade things like the Navigation Acts that helped Britain.
The change in British policy in 1763, then, was caused by the financial needs of the British government that arose from the Seven Years' War.
Great Britain changed some of its colonial policies after 1763 for several reasons. One reason why the British established their colonies was to make money. However, the colonies were becoming more expensive to run. After the French and Indian War ended, there was a growing concern that the Native Americans would attack the colonies. Most Native Americans were friendlier with the French. They believed the British wanted to take their land. Since the French gave the British some of their land in North America, the Native Americans were unhappy. As a result, the British needed to increase their military presence in the colonies to protect the colonists from possible attacks by the Native Americans. The British believed that since the colonists were benefiting from this protection, they should help pay for it. This led to new tax laws. The British also required the colonists to provide housing for the soldiers who were protecting them.
Another reason for changing its colonial policies is that the British realized that by not closely enforcing the Navigation Acts, they were losing money. Since it was becoming more expensive to run the colonies, the British decided to enforce these laws more closely. The colonists weren’t pleased with this change because that had been able to smuggle items into the colonies for many years.
Thus, the growing costs associated with running the colonies and the belief that the colonists were benefitting from the British presence were factors that encouraged the British to change some of its policies regarding the colonies after 1763.