The British military had many troops that were well trained.
Familiar with the land
The British's vast navy not only gave them a tactical advantage over overseas, but it also allowed them to transport supplies from all over the world (e.g. The Triangular Trade).
Determined to fight
The British had a globally known and well-established military, which subsequently meant that they were prepared with an adequate amount of supplies and weaponry to take on any competition who challenged their authority.
The colonists were fighting on their own land which means they could navigate better than the British.
The British soldiers were fighting because it was their job, but the colonists were fighting for the freedom of their country and its people.
Benjamin Franklin, Arthur Lee, and Silas Deane signed the Franco-American Treaty with Conrad Alexandre Gérard on February 6th, 1778. The French aided the Colonists in their battle against the British.