Germany wasn't partitioned per say but it was reduced in multiple ways to stop potential German revenge. For example most of Germany's neighbors got a slice of German land. I'm not sure where you are getting the polish partition from. WW1 created Poland it did not partition it. From this map you can see significant losses to Germany territory most importantly the Danzig Corridor which would serve partially as the reasoning for a German invasion of Poland in 1939.
This however was not the only step taken to prevent Germany returning as a world power. The German military was greatly reduced on all fronts from battleships to tanks and aircraft. Laws were put in place banning Germany from producing certain types of military equipment. Germany was also not allowed to keep troops in the Rhineland thus eliminating the possibility of a sudden German invasion of France (Along with the french fortifications built upon the French German border.) German colonies were seized by other great powers which also weakened Germany by reducing its availability of natural resources something Germany always lacked.
In conclusion the reason Germany was not simply broken apart was it was otherwise restricted and thought to be incapable of a renewed offensive. Of course hindsight is 20/20 and now we know it clearly did not work.
I'm looking everywhere for a post I did on this very question a while ago that went far more in depth but, in short:
Money
Stability
The French had the core of their industrial potential, Brie-Longwy, occupied and looted for 4 years. Their economy was in absolute tatters. The British, due to the Soviets defaulting on Tsarist debts, went from the worlds largest creditor to worlds most in debt in the span of those 4 years. The Belgians were little more than a vassal state to be sucked dry for resources of the war effort. All three of these countries were in absolute tatters and they needed reparations to rebuild. There's an attitude in 'pop history' that the reparations were punitive and just to spite Germany but they were very carefully calculated to be precisely the damages the German invasion was responsible for.
In fact, a lot of what happened to Germany was to be as helpful as possible to their continued stability. They (the Entente) needed a strong Germany and it was in their best interest to encourage one. Especially Britain who relied almost entirely on German industry imports. A significant amount of the land Germany lost would be to plebiscites, that is, the people voted to leave. Some even voted to stay! The biggest chunk they lost, Posen et. al, were just overwhelmingly ethnically polish but that's for another discussion if that was 'morally' okay or whatever. Regardless of that though their industry was left wholly in tact -- if they wanted to crush Germany to never rise up again that would have been what they would have struck.
However the goal wasn't revenge, or beating them down, the goal was stability. If Germany was splintered apart it would be absolute chaos. Bavaria alone seceded as a Socialist Soviet Republic on its own and there were secessionist movements and communist uprisings across the country for years after Versailles. Now imagine that Germany had lost its central infrastructure and military command -- Central Europe would have been dominated by Soviet satellite states from the get go. Now I'm not going to sit here and ramble about that being a good or bad thing in retrospect but, in the eyes of the democratic French and British and Americans, it was to them. So Germany had to be kept strong both to help rebuild the Entente financially and to expand democratic principles across Europe.
We can see throughout the 1920's and 1930's that the Entente just let the Germans walk all over Versailles time and time again. Reparations were halved, then forgiven entirely in 1924 and 1932 respectively with only a brief show of force in the former case. German rearmament went unhinged, German expansion went unopposed. More than anything else the Entente powers wanted peace and they felt peace begetted more peace, quite naively at that. It was their hope that a Germany who was kept relatively strong and had a good democratic government would be enough as, again, they hoped stable peace begetted more stable peace.
A wonderful book on this is Adam Tooze's new work, The Deluge: The Great War, America and the Remaking of the Global Order, 1916-1931
