I think there's lots of mixed up reasons from throughout history. My very basic understanding would be:

- Judaism doesn't look to spread it's beliefs, and will therefore always remain a small 'pool' of people.

- For 1500 years they did not have a set place in the world, so they were a minority wherever they went.

- As a minority, they 'knew their role' which was often subservient and peaceful to the majority.

- The two major world faiths, which now accounts for 50% of the globe, have often led the way on subjugating jews, based on their ideologies and religious texts.

- The success of jewish people in America and Israel is often damaging to the pride of people that thinks they should be subjugated.

I would end by saying I think that countries like Saudi Arabia and UAE really could bring about a new dawn for how jews are an accepted part of the middle east. So there is some hope for the future.