I think the correct assertion would have been that more Jews would have left. Even the information you linked to suggests that, at least as of 1938, many Jews weren't convinced they had to leave yet.
Emmigration is difficult, especially if you're in the middle class.
What would need to happen for you to abandon your job/business, home, extended family and friends and home to move to another country? I don't know what the answer is, but I think in a similar circumstance my first instinct would be to hunker down and wait for things to blow over.
If you're poor and striving, I think these decisions are a bit easier. My grandparents all immigrated to the US from Ireland between 1929-1946. For them, the complete lack of opportunity made it the only decision that made sense.
Spooky23 is probably also right - it seems easier to move if you're at the top (internationally known and/or could walk into a good new job) or at the bottom (nothing much to lose), but harder at the middle class.
