There were major issues with amphibious landings, but the bottom line is that even if the Allies landed behind the German lines, that would only be a temporary advantage; the Germans would quickly be able to throw up a defensive line, and there’s a new sytem of trenches in place.
Remember that the amphibious landings of Normandy and North Africa depended heavily on combined forces - co-ordinated by radio. In WWII, there were portable radios that individual infantry men could carry with them in battle. In WWI, a “portable radio” meant a unit that sat on a table.
As others have commented, the lack of communications always hampered an offensive break-through in WWI, because the commanders lost contact with the troops as soon as they were past a certain point. It then became impossible to coordinate the attacks, move the troops to hit a threat, and so on.
Plus, the troops would be moving on foot - they weren’t mechanized. That made a break-through very difficult to turn into a major advance.
The communications in the WWII landings were also crucial to coordinate the naval support, and the air support. That would have been completely lacking in a landing in occupied Belgium in WWI.
There are also technical issues. Air power was not as strong in WWI as it was in WWII, and range of aircraft wasn’t as great - and the coast of occupied Belgium was farther from Britain than the Normandy beaches. Could the RAF have provided much in the way of air support? I don’t know, but it seems that they would have been much more strained in the Belgian situation in WWI than they were in Normandy in WWII.
And the landing craft. The WWII craft were specially designed, using engine technology from the 30s and 40s. Could Britain have produced such specialty craft in WWI? I don’t know, but again I wonder if they could. Was the engine technology there for such small craft in WWI?
Then there’s also the factor that the defenders would have had the advantages of communications and transport. The Germans controlled the Belgian railways and telegraph lines, and could also use radio to some extent, so they would be in a much better position to coordinate the defence than the Allies could coordinate the offence. And, they would have had the advantage of short lines of communication for both their infantry/artillery and their air support, much shorter than the Allied aircraft could have had. Although the infantry weren’t mechanised, the Germans could have used the Belgian rail system to deliver troops close to the front, even if they had to march to the front itself.
And finally, the basic reason for the defensive stalemate: the machine gun. It gave a tremendous advantage to the defence. Even if the British and French could have successfully landed on the Belgian coast and started moving inland, it wouldn’t take much for the Germans to start setting up defensive positions. They would have been hastily constructed, true, but it didn’t take much of a defensive position to put machine guns into operation. There’s no reason to believe that just because the Allies landed amphibiously, they wouldn’t run into the same advantage for the defenders as on the Western Front. Once that happened, the Allies would have to resort to defensive measures, and then there’s a new trench system coming into existence, running east-west across northern Belgium, instead of north-south across Belgium and France.
And then, there’s the geographic factor: the trenches ended at Nieuwpoort, Belgium, which is on the western end of the Belgian coastline; that’s where the “Race to the Sea” ended in late 1914. Even if the Allies got a toehold on the other side of the trenches,they would be in northern Belgium. They wouldn’t be anywhere near Germany, but rather up against the Netherlands. That doesn’t help put much pressure on Germany, unless the Allies were prepared to violate Dutch neutrality, which seems highly unlikely. Plus, fighting one’s way across the Netherlands would give the Germans plenty of time to prepare their defences on the Dutch-German border, or even inside the Netherlands, as a pre-emptive strike.