>>64352164 (OP)
Linear warfare made sense; it only seems otherwise because an average person's understanding of it comes from pop history media made by equally uninformed people, and because they don't consider the limitations of period technology (in particular the absence of radios and smokeless powder)
>why lines?
first of all, that wall of bayonets is your only defense against getting steamrolled by enemy cavalry (or the enemy's wall of bayonets)
secondly, good luck coordinating five hundred dudes in any other way without radios
>why fire in volleys?
"accuracy" is probably the standard explanation, but that's not the full picture: it's more about effective range
an individual trained soldier with a smoothbore musket can reliably hit a dude up to about 100 yards, or maybe a bit further if he's really good; for context, this just happens to be about the same range a bayonet charge becomes viable at
put a bunch of dudes together, and collectively they can more effectively engage at significantly greater distances
>why brightly colored uniforms and banners?
because black powder: camo is largely irrelevant because the moment you take a shot, the big cloud of smoke gives your position away
a battlefield will get pretty smokey, so with that and the lack of radios, this is the only way anyone on either side will be able to tell what the fuck is going on
development of smokeless powder in the late 19th c. was very quickly followed by armies switching to more drab colors
>why musicians?
pre-radio comms relaying orders and signals
>did they just never think to try fighting like we do?
As it happens, they actually did: skirmishers/light infantry like in pic fought in a dispersed manner much more familiar to someone in current year, but due to already specified reasons, this was only viable in niche applications (e.g. harrassing the enemy, screening for the main body of infantry, or fighting in mountainous/densely forested terrain where cavalry is less dangerous)