Answer:
The British Empire was very wast and it was hard to concentrate only on the colonies. The big distance for the supply lines made resupply of troops and equipment very expensive and difficult for the British. They would need more than a month for shipments to arrive where Americans were fighting on their soil. The second thing was that the Americans were using Guerrilla warfare and had lots of experience and knowledge about their territory. This allowed them to turn the tide in many battles and they were supported by France that sunk in a lot of money to fight the British.