Every religion has its non-observant members.
1) Non-observant Jews may be under peer influence.
2) Convenience; desires. No one wants "bothersome" rules.
3a) Lack of proper information. People have inaccurate notions about their religion.
3b) Lack of Jewish education.
4) Unfortunate experiences. Someone who had a harsh religious upbringing or parent, may retain an unhappy feeling towards Judaism.
5) Many think that science, and specifically Evolution, have proved that there is no need for religion.
6) Intellectual laziness. Many people have simply never delved into the subject.
7) Stereotyping. People call us "religious nuts," etc.
Orthodox Jewish teenagers eat the same things all Orthodox Jews eat; kosher foods of all different kinds.
Lox is cured salmon but this is not specific to Orthodox Jews. Lox is the same regardless of its being kosher or not.
It depends on the level of observance. Orthodox Jews eat nothing BUT kosher foods.
Kosher food is not like a specific food. It is not like Hamburgers or anything. SOme foods are kosher and others aren't. Since most people eat all types of food, you can't really avoid eating kosher food.
Boys and men are given skullcaps for their heads and they learn the Jewish traditions and they eat kosher food.
Orthodox Jews don't, but Jews who belong to other branches of Judaism may or may not eat non-kosher foods, it's a personal decision.
Orthodox Jews keep a strictly kosher home.
Orthodox Jews
So long as the burger and all accompaniments are kosher, religiously observant Jews can eat it.
Orthodox Jews are only allowed to eat kosher foods.
Orthodox and Ultra-Orthodox Jews are strict followers of Jewish law.
There are many different types of Jewish people in the world, and many of them choose to keep kosher. The group that stresses keeping kosher and following the Torah the most are the Chassidic. See http://judaism.about.com/library/3_askrabbi_o/bl_simmons_chasidut.htm for more information