The proper question, is why would you want to NOT be Jewish? (if given the chance like a person with a Jewish mother)
I don't observe all the mitzvot.
But I will raise my child with knowledge of Judaism and Torah, because that is the best upbringing a child can have, also it will ensure that he has a Jewish identity and in turn passes that onto his children. I think it's the obligation of every Jew to marry a Jew and raise your children with a formal Jewish upbringing to ensure survival of the Jewish people. What keeps me in Judaism is the knowledge that HaShem is the one true G-d, pride for Judaism and pride for the Jewish people and our history.