Why were so few refugees able to flee Europe prior the outbreak of World War 2?

There were actually significant movements of Jewish refugees between 1933 and 1939. While it's true some countries made it difficult or impossible to gain asylum, tens or hundreds of thousands migrated to various destinations worldwide. Overcoming the hurdles to migration varied depending on circumstance and destinations, but included securing the necessary visas and travel documents, finding someone willing to provide sponsorship or employment overseas, and accumulating the funds for travel.