Isn't it because of the weapons? Without rifled barrels the bullet could come out flying all kinds of directions. If you were all hiding behind trees and other forms of cover, taking proper aim, the fighting would never end. Now if each side is just a wall of bullets going aginst a wall of people, you'd actually have a chance to hit something.
When it comes to comparing muskets to modern weapons, people get weird. They compare field-performace of muskets to the seller's catalog for modern weapons.
Soldiers back then got about 0 hours of marksmanship training, unless they were in whatever the country's version of Light Infantry was, so the average soldier was a horrible shot. So when people talk about the accuracy of muskets, they're mostly saying "Lots of soldiers would miss with this weapons".
Modern weapons are, if you fire from a table on a clear day, at least an order of magnitude better, and soldiers are signficantly better trained at shooting. And yet, the vast majority of shots aren't even remotely close to hitting. Nobody says things like "The accuracy of an M16 is 0.002%" due to the vietnam war taking 50.000 rounds for a kill, but this is basically the same thing.
Coordination requires communication. Instant communication was only possible within drum, trumpet, or semaphore range: a couple miles at best. Long distance communication was only possible by messenger.
Small units cannot be effectively coordinated against a massed enemy when your best communication method is some dude with a horn. Until the telegraph and telephone allow for trench warfare, Napoleonic big-unit tactics are the best we can expect.