An important thing to note is that trench warfare did not completely disappear from warfare in WW2, it just lost its primacy as the main focus of the war. Instances of trench warfare can be found on the Eastern Front and in Italy with the Winter Line used to try and slow the allied advance in Italy.

But two major factors contributed to the change in warfare tactics in the period. One, which you alluded to in your question, was mechanization and improvements of technology that made mobile warfare easier. The second was the development of new tactical and operational doctrine in the decades that led up World War Two that heavily focused on breakthroughs and mobility.

The first part is the easiest to address. In the years between the end of World War One and the start of World War Two saw massive improvements in vehicle and aircraft technology which aided in offensives and mobility of large amounts of forces. The armies of the First World War utilised trains or marching as the main way to get to soldiers to the front. Marching obviously takes long amounts of time to get men and supplies to the front and exhaust troops the further they march meaning eventually they have to stop. Trains can be useful for mobility but are reliant on tracks to move. This means that where they can go is limited and also easily detectable by the enemy. Armies still relied on heavily on pack animals to pull supplies through muddy terrain to get supplies to the front as trucks were slow, small, and got stuck easily.

Planes were also still fairly new tech and limited capability to affect troops on the ground beyond recon or light machine gun fire with some planes. Bombing was fairly experimental and not extremely effective, with it mostly being pilots dropping bombs out of their cockpits as they flew over the enemy.

Tanks, which first saw action by the British at the Battle of the Somme in 1916, remained rather crude and were fairly unreliable, got stuck often, and not always the most effective in pushing offensives. Tanks only advanced a little more than a walking pace, having no real speed due to weight and inability to effective traverse difficult terrain. Tank armor also was in its infancy, with mortars and artillery eliminating tanks with relative ease. Specialized 8mm K-Bullets from rifles could even punch through the tanks armor.

Forty-nine tanks were shipped by the UK to France for the Somme offensive, in which only thirty-two could take place in the initial first wave and only nine made it successfully across no man’s land. France was super critical of the British for using the tank as they had seen its effect as indecisive and giving away any secret advantage it could have had in the future. Other nations had little success with tanks as France, while having some larger designs, mainly used smaller designs like the Renault FT-17 which had limited firepower capability. Germany only made 18 tanks, a large difference from the tank reliance they had in the Second World War.

Compare this to World War Two in which planes became much faster, even seeing jet fighters, with more accurate and reliable ways of delivering payloads. Look at the difference between a Gotha G.V. German bomber from WW1 and a B-17 Flying Fortress from WW2 and they difference is astonishing. Dive bombers such as the Junker Ju 87 (commonly known as the Stuka) made attacking ground defenses easy and allowed planes to better assist in ground offensives.

Tanks became faster, more effective in firepower, more armored, and specialized with distinct classes such as medium tanks, heavy tanks, and tank killers giving more tactical flexibility and usefulness. Even heavy tanks like the German Tiger tank could reach speeds of 28 mph on roads and 12-16 mph off roads, all while being more well armored and armed then any tank of World War One. Compare this to the speed of a British Mark IV tank of World War One that reached a little over 4 mph and its clear to see how advanced tanks had become in a little over twenty years. Also tanks were produced in much larger numbers with each nation making thousands of tanks meaning they had a larger impact on the battlefield. Even general vehicles like supply trucks and troop transports became faster, more reliable, and in larger numbers meaning men and supplies could be moved up to the front faster and allowing more mobility.

Beyond the improvements in technology was the focus on mobile warfare. The generals of World War One went in expecting fast mobile warfare and engagements over long distances (as evidenced by the generous sightings of guns from the period). Its why many were surprised when World War one was not resolved in only a few weeks or months and lasted 4 years. A Large part of why WW1 became so static was the effectiveness of machine guns and artillery for the defense. Machine guns and artillery made it super costly to push any offensive and limited the breakthrough potential of infantry just running across no mans land.

This is where new doctrine comes into play. Many wanted to avoid the same static warfare of World War One. New Operational planning emphasis deep penetrative actions that utilized the newly matured tank technology combined with close air support and mechanized infantry in cohesive combined arms warfare. For the Germans this was Bewegungskrieg (Maneuver warfare) with the goal of gaining a Kesselschlacht (cauldron battle) that resulted in surrounding the enemy until they surrendered or were annihilated. Bewegungskrieg and Kesselschlacht were not new ideas as they were used by Moltke the Elder during the German wars of unification, however it’s the implementation of new airplane and tank technology that was new and resulted in its success in making World War Two more mobile. Russia had similar ideas with their Deep Operations which had the goal of exploiting tactical success to push deep into enemy lines and disrupt their logistics to effect the enemy at all levels of their line, not just the front. An important factor was having infantry just as mobile as the tanks and planes. Tanks are great for breaking through but cannot hold ground or territory on their own. Using troop transports to move infantry along with the tanks aided in offensives. Instances where tanks outran the infantry's ability to keep up such as what happened with the Germans on the Eastern front lessed the offensives effectiveness as tanks were exposed or had to wait for infantry to catch up.