Furthermore, it should be noted that when it came to RAIDS and other hit and run attacks (mostly on lightly defended outposts and unprotected farms or villages), Natives DID this.
My friends, this is a world without radios. Or modern combined arms tactics. Infantry and cavalry communicate by instruments - drumbeat, flutes - and standards. Visibility is IMPORTANT.
And THEN, in the rout, the regulars charge.
Think of, essentially, a giant phalanx with REALLY REALLY long spears.
What changes is George Washington hires one of Europe's best drill instructors to train his men
Professionals do in fact train to deal with amateurs!
1: America is huge and wealthy for a set of rebellious provinces.
2: Some legitimately talented, dedicated leaders and allies, ESPECIALLY drawn from Europe in the form of Steuben and Lafayette.
3: Britain was busy.
And when France joined the war, Britain was suddenly facing a World war. The colonies weren't worth it.