> apparently they waited outside a few weeks to give the Germans time to kill as many remaining civilians as possible so they could set up shop themselves
That's... a misrepresentation of a complex historical event, to say the least. Polish government-in-exile made a bet that Home Army forces could overthrow Germans on their own and restore 1939 border with Soviet Union. And Home Army explicitly planned Operation Tempest to be executed before Red Army liberated the whole Poland. Should they succeeded, Soviets would have to negotiate with a sovereign Poland, instead of coming there as a heroes-who-liberated-Poland-from-Germans.
As the history goes, the bet failed an the uprising was drowned in blood. But it's stupid to blame Soviets for not helping the regime which was profoundly anti-Soviet.
History knows no ifs, but should Poles cooperate back then, probably they could achieved the same result with a lot less of blood.
https://en.m.wikipedia.org/wiki/Warsaw_Uprising