Answer:
2 main reasons: Better Weapons and types of warfare
Step-by-step explanation:
So one of the biggest reasons for the larger loss of life in WWI was the newer weapons, aka the muskets verses machine guns. Machine guns are clearly faster and more effective weapons and continous rapid fire whereas the muskets were single fire and required the user to reload and be exposed. There were the use of tanks and submarine warfare as well, which were new and had not been seen in war before.
Secondly, there was the use of trench warfare which seemed like it was helpful since it was supposed to shield soliders from war but ended up being a cesspool for bacteria and manifested in diseases.