Various reasons:
1) Some Christians, including a few politicians, believe that Jews have to be present and in control of that land so Jesus can return, kill them all and send them to hell.
2) White European Jews are overly represented in key components of America society given their total population (~3-5 million out of 307 million): business leaders, media, entertainment, banking, economics, government, judicial branch, wealthy. Not all of them are Zionists, but a good majority support their own (as most groups do). A lot of it has to do with discriminatory hiring or promotion based on essentially favoritism. A lot of it has to do with historical access to money (Christians and Muslims were forbidden to engage in interest loaning of that kind for quite some time). A minority think that these White European Jews are genetically superior in some way. Whatever the case may be, there is no doubt that white european jews make a good chunk of the ruling class in America. All oligarchies serve to appease the ruling class by definition.
3) AIPAC is a huge lobbying firm with a lot of power. They can make or break politicians. They provide free vacations to Israel for congressmen.
4) Censorship in the media, blackmailing, and threatening of career suicide.
5) Some people see Israel as the front-line to the War on Terror
6) Some people see Israel as the only true ally in the region. The sole democracy that happens to provide massive amounts of intelligence to the US.
7) There is a small number of Jewish politicians who pretty much govern as representatives of Israel. For example, in New York State, a politician essentially proposed a bill to gut the 1st amendment because he didn't like the student body of an educational institution protesting Israeli government policy.
It's important to note that not all Jews fit into this. There are black Jews, Sephardic Jews and non-Zionist Jews who don't benefit at all. Anti-Zionist Jews are often blackballed or marginalized all the same, regardless if they are of white European ancestry. Even in Israel there is a minority of Israelis publicly protesting their government and their invasion of Gaza, and they are receiving major backlash and non-coverage.