This is because their peoples were not entirely conquered.

Let's take France, while the germans conquered homeland France, the French still had a sizeable colonial empire which came with a sizeable army over seas, not all French soldiers recognised The Vichy Gouvernment imposed by the Germans so a considerable chunk of the French colonies decided instead to join the forces of Free France siding with the allies, with them came about a quarter of forces which had succesfully retreated at Dunkirk, contrary to popular belief, most of the French troops over seas refused to side with the Free French army but the free french army relied on native populations for most of its forces, these came from West African French colonies which due to strong trading links with Britain chose to side with the allies. While the land forces where reluctant to serve the allies, the naval forces where more disident and by 1940 more than 50 warships in diferent corners around the world had chosen to pledge their alegiance to Free France. Thus the French rallied under Charles de Gaulle would go on to support the allies in North Africa and set up the crucial network necesary for the french resistance to operate.

As for Poland, after it was ocupied by the Germans and soviets many soldiers fled the country and established the polish gouvernment in exile, about 80 000 troops fled to France, after the fall of France about 35 000 managed to flee to the UK, they where joined by another 4000 troops and volunteers in French Syria which had escaped through Romania, their ranks where further bolstered by the war between Germany and the USSR. After the soviets ocupied Poland, an aproximate 1.25 milion civilians where deported in Siberia and Kazahstan, when war with Germany broke out, the soviets where forced to side with the allies which meant that they had to release their prisoners, these refugees made theyr way to Iran where they joined with the established polish forces under British supervision, the civilians which joined the British would form the Polish Army in the East or Ander's army. At its peak the polish free forces counted 249 000 soldiers.