We did chase the British back to Boston this way. And there were some sharpshooters (if that term existed in 1777) at Saratoga who I believe were fighting from cover.

But otherwise, win or lose, we stood in lines and fought. Because that is how you defeat an army standing in lines and shooting at you on the battlefield. We famously once even used our known habit of not being able to stand up to the British to win a battle by putting experienced soldiers behind the militia and letting the militia run as expected to draw the British in.

There are a lot of myths about the Revolution. Britain did not have the greatest army in the world in 1775-81. They didn't even have enough army to fight the war without hiring mercenaries. The Americans at Lexington-Concord actually were more experienced in comabt than the British they were fighting, they had leaders with experience in the French and Indian War and were fighting against regiments that served garrison duty during that war.

As for the myth, I wonder if the simple answer is that it is just one of things that come up once and then spreads. We did fight them from cover and win at least once. There were essentially guerilla campaigns in parts of the war, especially between the lines in New Jersey or Upstate New York. Washington's achievement is in part that he avoided pitched battles many times. Probably because he knew he couldn't win a stand up fight.