Attack on German forces distracted by uprising, with safe places to move through the river secured by rebels would be easier and faster than waiting for Germans

Attack on German forces distracted by uprising, with safe places to move through the river secured by rebels would be easier and faster than waiting for Germans to mop up and destroy the city. And of course Stalin warned against uprising - he wanted to get Poland, any independent forces were a threat to that plan. After WW2 he imprisoned anti-nazi guerilla fighters in Poland and murdered their leaders in a show trial in Moscow (after promising them safe passage).