The Belgian coast was a complicated problem for the Royal Navy. This map shows that the flanking movements on land ended around Nieuwpoort, Belgium.

The main German naval base in occupied Belgium was Bruges, which was connected to the sea by canals to Ostend and Zeebrugge. Bruges was well behind the front lines, and inland enough that it could not be knocked out by a naval bombardment. That means that Germany could freely deploy their destroyers, torpedo boats and subs to pretty much anywhere along the occupied Belgian coast quickly, without fear of prior molestation by hostile naval forces. Obviously you cannot land an amphibious force within 10 miles of Ostend to support rear operations with this threat.

One British vice admiral hatched a plan to attack these outlets, Zeebruugge in particular, with heavy-gunned monitors, but the plan wasn't accepted. It took them until 1917 to figure out a plan to neutralize that German naval presence, and even then it didn't work. In the Naval Battle of Zeebrugge and Ostend, the British filled a couple old cruisers with concrete to form blockships at the entrances to the canals. The main objective was to be carried out under the cover of a diversionary raid on the seawall around Zeebrugge using a modified cruiser carrying Royal Marines. A bunch of marines got medals for valor, the British made a show, but they weren't able to completely block the access to the canals.

In short, if mounting a raid to try to sink three of their own ships in enemy waters was such a challenge for the British in 1918, a real amphibious landing against defended beachheads would probably be unthinkable, especially after Gallipoli.

Britain had sea superiority to the extent that the German navy was essentially contained in its own waters

Nonetheless, I suggest that their superiority was not so complete that they could easily launch an amphibious operation in coastal waters close to the enemy's bases. Remember, to protect an amphibious landing it is not sufficient merely to "win" the ensuing naval battle by sinking more ships than you lose; you have to prevent the enemy from getting even a single heavy cruiser in among your vulnerable transports. Transport ships are not armoured; six- and eight-inch shells will wreak total havoc. This is why, in WWII, the British were so worried about the four or five major surface units the Germans had getting out into the Atlantic, while several dozen submarines were more of an attritional nuisance; a sub sneaks in and snipes one or two merchantmen at a time, but a battleship can sink an entire convoy in an hour of shelling. (Which being said, the Germans did have subs in WWI as well; the prospect of keeping the extremely expensive capital units of the battle fleet loitering about in shallow water for days on end, close to the U-boat bases, probably did not fill the Admiralty with joy.)

So, step one, prevent all heavy enemy combatants from getting in to interfere with your landing. Step two, keep the landing supplied, noting that at least initially you are presumably doing so over the open beach rather than a harbour. (Remember the Mulberry harbours of 1944, and note that they didn't work as well as the Allies hoped; the Normandy armies were somewhat short on supplies until Caen finally fell, a month after schedule. Plus, of course, you've now got to run convoys through a Hochseeflotte that's much more formidable than the German navy of 1944; it's true that the British didn't lose any ships in the Channel in the Great War, but it's also true that a Belgian landing would be, again, that much closer to the German bases.

Finally, having got your landing and supplied it, what are you going to do with it? The Germans can reinforce whatever units they have on the spot through an excellent and intact railway network, not the bombed-out remnants of 1944 - and let's note, Normandy was still a pretty close-run thing, which might have gone the other way if the German high command had released the powerful units they were keeping in reserve for the expected landing in the Pas de Calais. It seems likely that you would just create another horrible barbed-wire entanglement, and give the Germans the gift of internal lines - they can now shift troops on railroads between the two fronts faster than you can rail to a port, embark, ship, disembark, and rail to the front you want to reinforce.

I'm no expert but from my understanding almost all amphibious operations up to that point in history (other than Veracruz in the Mexican-American war) had been failures. The allies tried something similar to this against the Turks at Gallipoli in 1915 and it was a disaster

This also makes me wonder if there were any attempts by the Entente to make The Netherlands enter the war?

The short answer is that they did. The so called "Race to the Sea" in the fall of 1914 was the result of both sides attempting to envelope the other from the North that went back and forth until they reached the Belgian Coast.

The British actually did seriously consider an amphibious landing on the Belgian Coast several times, but postponed them to allocate resources to other areas. Furthermore, the Germans had heavily fortified the Belgian Coast, and the British experience at Gallipoli had made them wary or amphibious invasions.

The most serious plan was Operation Hush in 1917, however, it was dependent on the success of the Battle of Passchendael. It was cancelled when that offensive was not able to meet Hush's requirements.

Thanks, all, for the solid replies!

I think the answer is simple military tactics held over from the Napoleonic era. Since the invention of the army the goal was simply to put enough pressure on one area of land with your army to remove the opposing forces from the field of battle. Your objective was always to put a critical mass of fire/troops to force the enemy in that area (and hopefully all troops on the field) to retreat or surrender. After enough ground is lost by one side or another they would usually agree to stop fighting - usually to the benefit of the side that gained more land. War!

WWI was the first war where it was literally impossible to use the tactics that had worked for millennia. Because of the machine gun it was prohibitively costly to put enough soldiers in one part of the field to "break through". Even if you used the new artillery to try to help your advancing troops - they simply retreated a short distance until the advancing troops ran out of steam.

The First Great War devolved into trench warfare - a stalemate - because neither side could get over the old style tactics of war. They set up a line of Defence from the English Channel to the French alps, and organized many attempts to "smash the line" - a tactic that had been viable since ancient warfare - to little or no success. Troops that were overrun could simply move back to the next line of defense and hide behind a wall of machine guns and artillery cannons. Flanking was impossible because there was no way to go around without 1) expending many thousands of troops per yard gained and 2) leaving huge gaps in the line, exposing them to actual defeat.

TL;DR: Military technology evolved faster than military tactics and the old men in charge of the armies still using 19th Century thinking.

Source: The Guns of August by Barbara W. Tuchman