In what way did trench warfare turn out to be a disadvantage to both germany and the allies in the war

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. 

Are there any answer choices