Why did world war one soldiers wear puttees?

Puttees were worn to protect the legs from superficial damage from brambles, spent ammunition and hidden obstacles. They were worn so as to keep the trouser bottoms contained so as not to cause tripping. They also kept sand and pebbles out of the boots. They replaced gaiters which were leather versions of the same item. Unfortunately, leather gaiters were stiff and restricted mobility. Puttees on the other hand were cheaper and provided the kind of protection that foot soldiers required. To this day, modern soldiers wear a type of puttee modeled after the short puttees of the 2nd world war. They are worn with KD shorts and worn for looks to transition the boot to the knee sock.