Alright so as we know prior to the first world war the world was dominated by a number of massive Empires. The British Empire, Russian Empire, German Empire, Ottoman Empire and the austro-hungarian empire. Yet when the first world war would come to an end all of these Empires aside from the British Empire would no longer exist. Why?
What was it about the first World War that caused the deaths of so many Imperial powers? Now you could say that some of these Empires were already on the downturn. After all the austro-hungarians and the Ottomans were already starting to suffer pretty significant cracks in their imperial system. This of course was also happening to a slightly lesser degree in Russia with the widening gap between the peasantry and the aristocracy.
Yet the German Empire was surprisingly stable. Yet somehow at the end of the war Germany lost pretty much all of its Imperial Holdings. One thing that is terrifying is the fact that this was actually predicted by Otto von Bismarck. And his prediction was only off by about four months.
Still. I fail to see why so many empires fell during this short time.
You left out the French Empire, the Italian Empire, the Japanese Empire, and the American Empire, which all either survived or thrived.
The narrative of the declining/decrepit Austro-Hungarian empire is well addressed by u/kopz in this post.
There are two main drivers of the fall of the German and Austrian empires. The first is that the winners wished to impose their government forms, having used the Imperial figures as propaganda points during the war with their public. The reality was that the German Reichstag and Bundesrat represented a powerful force in German politics that was growing stronger, not weaker, and the Kaiser did not "rule" Germany in the way that some wish to believe. While the Kaiser was not a figurehead, Germany was far from being governed by decree. Austro-Hungary was also largely governed by local or regional authorities and not by the dictates of a distant emperor. That didn't stop the change of government and break up of Austria-Hungary from being central demands of the Allies.
The second, and equally important, is that the extreme duress of the war, as experienced by residents of Austria-Hungary and Germany (and, indeed, Russia) caused a complete collapse in social structure and the public faith in the existing government. Hundreds of thousands of civilians died of starvation or malnutrition related disease as a result of the British blockade. Even had the allies not demanded a change of government, it would be easy to speculate that the existing governments would have collapsed anyway. Alexander Watson explores the societal impacts of the war on the homefront in Ring of Steel.
I suggest to you that if you placed Britain under the same stress as Germany or Austria, and have thousands of citizens dying for lack of food in a war you lose, that Britain's government would collapse as well.