Because there are 200 Christians for every one Jew in the world, and as a result we're somewhat sensitive about losing our identity. We already have a religion that's served us pretty well, we don't need yours, so please don't try to convert us.
If we believe our own religion, it is our solemn duty to try to convert you. Would you deny us our right to practice our religion?
Why don't the Jews try to convert the pagans and the Christians? If your religion is true, one would think you would want to convince as many people of the truth of that religion as possible. Instead the typical response to Christian evangelicalism is to bury your head in the sand and pray that the evil Christians won't come and shake your faith and steal your identity. Then the funny thing is that whenever a Jew finds peace in Jesus, you reject him and no longer number him among your people.
If Judaism holds the truth, then where are the Jewish evangelists? Why don't Jews seek to find converts among the gentiles? Is this a private club?
Amen!