War reparations are paid for actual wars and when some peace agreements after the war agreed that there are any war reparations due. Poland cannot just invent a claim for some occupation that was indeed result of Russian imperialism covered in communist clothes but was much more complicated and involved Polish domestic communists as well.
Soviet Union was on a victorious side of WW2 and hence there were no talks of reparations for the Soviet war of 1939 against Poland. This war was not to be mentioned at all and Poland was shifted westward to the Oder/Neise border instead, into areas that belonged to Germany.
On the other hand, there were actual war reparations agreed after WW2 during the peace talks. They were later mostly abandoned by the claimants in order to not repeat the Versailles and to make the reconstruction of Germany possible. For the eastern bloc countries this was more complicated. Czechoslovakia expelled Germans from Sudetenland and hence got their property instead. The reparations claim was basically settled based on this (and hence any restitutions of individual properties lost by former German citizens of Czechoslovakia were ruled out even after 1990) . Poland,however, had a more complicated situation "Poland was to be excluded from the proceedings of the IARA by demand from the Soviet Union. The Allies agreed as part of the Potsdam Agreement, that the Soviet Union collects and distributes the Polish share of reparations. Furthermore, the Soviet Union would extract its share of reparations mostly from the territory in its own occupation zone." (the linked Wikipedia).
They key is that those reparations for multiple countries were collectively agreed by the peace talks by all sides of the Potsdam conference, it was not just something Poland would invent because it thought it deserved it. Whether it makes sense to demand the reparations now and from Germany (not Russia instead - based on the post WW2 provisions) and the current validity of the claim is a different question. To a layman, it may seem that those extensive areas that Poland got could be quite sufficient instead.