The peacemakers had other objectives in mind apart from self-determination

From The Long Shadow: The Legacies of the Great War in the Twentieth Century by David Reynolds.  Page 13.

Germany maintained its identity when the Hohenzollern dynasty was overthrown, but the Reich had its wings severely clipped, losing 13 percent of its prewar territory and 10 percent of its population.25 On the southwest, Alsace and Lorraine, won in the Franco-Prussian war of 1870, were handed back to France. To the east, Germany surrendered most of Poznan, West Prussia, and the Upper Silesian coalfield to the new Poland, plus a corridor allowing Poland access to the Baltic Sea but thereby separating East Prussia from the rest of Germany. Three million Germans remained in the new Czechoslovak state, while the peace treaty with Austria explicitly barred its now overwhelmingly German population from a union with Germany (Anschluss). None of this was easy to square with the principle of self-determination. Similarly, three million Hungarians lived outside the rump state of Hungary, half of them in Transylvania, which was occupied by Romania in 1918. The Allies duly ratified this land grab: their dislike of Hungarian autocracy was compounded by the country’s brief but alarming Bolshevik Revolution in 1919. The German and Hungarian settlements were reminders that the peacemakers had other objectives in mind apart from self-determination, especially punishment for the defeated and security for the victors.

Interestingly, this is evidence supporting an argument by Joseph J. Ellis in American Creation.  

The founders opted for an evolutionary rather than revolutionary version of political and social change, preferring to delay delivery on the full promise of the American Revolution rather than risk implosion in the mode of the French Revolution. Although it is difficult for many modern-day critics to acknowledge the point, this deferral strategy, far from being a moral failure, was in fact a profound insight rooted in a realistic appraisal of how enduring social change best happens.

The wisdom of the American Founding Fathers in deferring unresolvable issues to be addressed later in time required the moral courage to create something less than perfect but did create something good enough for the times.  But they did not, deferring the bloody resolution into the future.  

The victors in World War I also deferred into the future the fulfillment of the principle of self-determination.  That deferral, similarly resulted in bloody resolution in the future.  

In both cases, there was a departure from foundational Classical Liberal principles in order to achieve the good enough instead of the perfect.  Both decisions were clearly wrong in principle and both resulted in tragic later loss of life.  But both created the time and space for further evolution rather than the possible collapse into division and anarchy.