Respuesta :

While being easy to  make and could hold many men, easy to defend and never really needed lots of men to defend them , trenches were actually extremely hard to get in and out of without being seen by the enemy, also cold, and wet, in turn the men on both sides would develop a infection called "Trench Foot"  that would require amputation. 
People were getting sick and it took much longer to move and attack either side causing the war to be extended