I’m under the impression that the Polish nation survived under Soviet oppression
With time, they would’ve killed it, with deportations, settlements, language policy, etc. Poles are more numerous than e.g. Lithuanians but Russia has wanted to Russify the whole area for centuries now. And the Soviets were nothing but the continuation of the genocidal, colonial, Russian empire with a different coat of paint.
They probably would’ve treated Poland like Ukraine and worse right from the start if the Nazis hadn’t tried a very similar thing directly beforehand: Poland had a very active and well-organised resistance, had the Soviets started out with their usual genocidal programme the Polish resistance would’ve fought right back. So they bid their time, first carefully cultivating an image as liberators.