I get the impression from talking to Jews that they don't expect obedience to the Torah from people who aren't Jewish.So if you convert to Judaism, then you have the responsibility to follow the Torah, in all its aspects, which they don't really want to saddle people with. They would rather your follow the basic moral code that underlies the Torah. It wasn't that way in Jesus' time, however, because you had people going out all around the Gentile world and winning converts. This is something that Jesus complained about:
Mt: 23: 15 “What sorrow awaits you teachers of religious law and you Pharisees. Hypocrites! For you cross land and sea to make one convert, and then you turn that person into twice the child of hell[f] you yourselves are!