The British overall had more supplies and weaponry than the Continental Army. One example of this is at Bunker Hill, where the Continental Army lost the battle as they had run out of ammunition, and had to retreat. The Continental Army would have won this battle if not for their lack of ammunition.
Compared to the Continetal Army, Britain had troops that had experienced fighting beforehand, most of which fighting, as well as respecting and following the orders their commanding officers.
Best Navy in the World at the time
The British had the best Navy in the world, and the Navy of the Continental Army didn't have a chance winning any battles against the British in the waters. Using the Navy, the British would also be able to fire at shores.
Compared to the Continental Army, the British soldiers were not nearly as passionate, as they were fighting under the orders of King George III, while the Americans were motivated to fight by the promise of liberty and freedom from the oppresive British.
Soldiers weren't as passionate about winning the war
We're losing the war!
Unfamilliar with area
The British army were not as familiar with the area as American troops.. This meant that the American troops would know the fastest routes as well as routes they could use to surprise attack the British.
where am I?.,..
Fighting the war from across the sea
The British troops had to be sent from Britain to the colonies, and this meant that it took a long time for troops to arrive as well as money, as ships needed to be sent back and forth, as well as have ammunition and supplies for the troops to use on them.