A little known fact is that Judaism is a highly mystical
religion with roots
in many spiritual philosophies
that seem anachronistic
to today's society.
One of the most basic principles of Judaism is that different people have different souls - in other words, if you weren't born Jewish you don't have a Jewish soul and thus have no business trying to convert.
This knowledge comes from the deep dark recesses of kaballa, and rests heavily on the belief in reincarnation - not something that those in the know are very keen to distribute among the uninitiated, since it conflicts with many of the more mundane practices of practical Judaic lore.
This is the combination of reasons why, when confronted with would be converts, the various religious authorities are both unsympathetic and inscrutable. In fact, I know of cases in Israel where people who wanted to convert in order to marry to Jewish people were asked by the rabbis to separate from their partners for up to two years, to test the strength of their conviction and to make sure it isn't just a romantic gesture on their part. The religious studies are rigorous, too.
I have to say, though, that the few people I know who did convert to Judaism and chose to lead a religious life in Israel are some of the biggest fanatics and zealots I ever met. Makes a weird kind of sense, I guess.