In reply to why? by Matthew
I beg to disagree. It is most certainly not straightforward. Most (that means over 50%) of immigrants have not been strongly or even moderately religious. Many have been more or less effectively secular.
Just consider the great Russian aliya. Many many non-Jews. Lies, false documents, the thinest of ancestral threads. Even some genuine neo-Nazis. Anything to get out of Russia or the Ukraine.