The answer to this question lies in part in the distinction between line infantry and light infantry. Only one company in a regiment was trained as skirmishers, the rest being trained to close to close range, fire and charge with the bayonet. European engagements were fought at very close range as the smoothbore musket is a fundamentally inaccurate weapon - but when you have a few hundred of them firing from 20 or 30 meters it's a fearsome wall of lead coming downrange. I think part of the reason this reaction seems odd to you is the scale - platoons as we have now are much smaller than basic command and control units on black powder era battlefields which tended more towards the company or battalion level. This is important because of another element we dont tend to consider because it's so anachronistic- cavalry. Even light cavalry will ride right over the top of musket armed troops in skirmish order, but no horses are inclined to ride into a wall of 500 bayonets in a square.

All of which is not to say that the experience of the French/Indian war and revolutionary war had no impact on military thinking. You can see this in the establishment of small bodies of troops armed with far more accurate rifles (most famously the 95th and the light battalion of the Kings German Legion), and in the tendency to pull the light companies out of line battalions to form distinct battalions and occasionally whole divisions of trained skirmishers.

Theres a saying in Military history that "every general tries to fight the last war". The point at which it really became apparent that the weapon technology had made maneuvering large blocks of troops around redundant was the decades between the American civil war and the Boer war.