More can always be said, of course, but I commend to your attention the appropriate section of the FAQ, specifically the headers 'Why did European armies use Linear Tactics?' and 'Mechanics of Linear Tactics'.

Adding onto that section, a few more posts:

• u/StoryWonker has an overview of the relevant factors;
• u/dandan_noodles looks at the dimensions of combat;
• and on the degree of risk and likelihood of lethality;
• and in conjunction with u/PartyMoses, the relative risks of being in formation;
• PartyMoses also covers the dimensions of combat;
• also how the fighting should go, according to one contemporary theory;
• and on a common idea, why the troops don't duck/get down/lie down/similar.