I know they were the odd cases where trench warfare was used in WWII, but why did it not turn into full scale trench warfare like in WWI?
^ These answers I've given should be pertinent
I know they were the odd cases where trench warfare was used in WWII, but why did it not turn into full scale trench warfare like in WWI?
The thing is, full scale trench warfare was only really a thing on the Western Front, and then it was only really from late 1914 to early 1917 at least. In WWI, the Eastern front, the Middle Eastern Theatre (with the exception of Gallipoli), and the Balkan Theatre saw trenches used as temporary positions and field fortifications at a tactical level, but the fighting was largely mobile. On the Western Front, the similar size of the armies, the small size of the front, the technology possessed by both armies and the well developed lines of communications meant that it was difficult to break into an enemy position, and even more difficult to keep up momentum and break out. It wasn't until 1917 that tactical methods and materiel was sufficient enough to ensure success at the tactical level, and it wasn't until 1918 that both sides possessed the significant reserves needed to create operational mass and then conduct maneuver.
In WWII, mechanization and motorization of transport, sophisticated radio communications, aircraft for air support and reconnaissance, and even more sophisticated artillery meant that it was far more difficult for a static front to solidify, but as you acknowledge, it was not impossible. The Weygand-Maginot Line, the 2nd Battle of El Alamein, the Eastern Front in Northwestern Russia, the German defense lines in Italy, June-July 1944 in Normandy and the fighting along the West Wall/Siegfried Line that year all saw static or almost static fighting. Inclement weather, evenly matched forces, poor command and control and logistical difficulties among other things, and in some cases a combination of these factors, helped to contribute to these static conditions, which lasted a few weeks in the case of the Weygand-Maginot Line, to three years in the case of Northwestern Russia.