Because there is no "they" and there is no "conspiracy" so there is no "control."
There is a difference between a large number of Jews being Hollywood and some boogeyman "the Jews" controlling hollywood.
Its VERY offensive, and, quite frankly, the fact that you don't get it creates a lot of questions about you.
It denies the INDIVIDUALITY of these Jewish people. It suposes some sort of group think and conspiracy theory.
It also implies dual loyalties and some nefarious plan.
By the way, what exactly is "controling Hollywood" anyways? Did the Jews control Hollywood to nominate the Pal Arab suicide bombing glorification flick, paradise now, for an oscar and Golden Globe (it one the later). How about producing Faranheit 9/11 (which is anti-Israel) or did the Jewish Actress get put in Passion of the Christ as a spy? Come on!
It is an anti-semetic canard, nothing more. There is NO SUCH THING AS "THE JEWS." "THE JEWS" doesn't exist. Its like saying "the Blacks" or "the Christians" or "the Muslims" - as if they were a monolithic whole.
Now, you could cite some Jews who share a specific ideology, but you have to get pretty darn specific to get to a coherent group.
Why are you resisting the idea, the very simple idea, that there just happen to be a lot of people of Jewish descent in Hollywood - probably because it attracts creative thinkers who are willing to take risks, and Jews have a lot of those in their population.