Nick Malik's answer to In World War I why didn't countries bypass trenches by landing troops beyond them? - Quora
"The use of ships to transport large invading armies was a "new idea" and militaries are run by old men.
Today, we understand and accept the idea of the Marines, but in 1914, moving whole armies that way was novel.
Traditional military services were segregated and very few "troop transport" ships existed. Remember that many world navies still fought pitched sea battles. Last thing you want, when a ship sinks, is to take both your navy and your army. Armies didn't trust the navy, and vice versa.
with so many structural reasons, it was not an idea that would fly."
Joel Parker's answer to In World War I why didn't countries bypass trenches by landing troops beyond them? - Quora
"There wasn't a lot of open beach to land in Holland & the German North Sea coast. The Rhine estuarine plain has been largely canalized through Belgium and the Netherlands, & German coastal cities were heavily defended with extended fortifications & huge coastal defense guns. Perhaps France could have been invaded but as noted here amphibious assaults on a large scale were unprecedented & considered too high risk for success."
Kyle Murao's answer to In World War I why didn't countries bypass trenches by landing troops beyond them? - Quora
"whereas the Nazis had kind of a wimpy navy, the imperial German navy during WW1 was enormous. If the Allies had attempted an amphibious landing of the scale required to achieve a strategic breakthrough, it might have been necessary not only to bottle it up in port, but to destroy it outright--something the RN had singularly failed to do at Jutland in 1916, where the Germans fought the British to a tactical standstill. German U-boats would also have posed a big threat to slow-moving troop transports crossing the Channel or the North Sea."