Despite their outward religiosity, why is Israel a predominantly secular nation?

The Bible says that Israel's return will take place while they remain in their unbelief. The change of the people of Israel is described in Ezekiel 36:26: “A new heart also will I give you, and a new spirit will I put within you: and I will take away the stony heart out of your flesh, and I will give you an heart of flesh.” Notice that this is a “new” spirit, not “His” spirit. The Jews who return to Israel will experience a change, but not a conversion. They aren't coming back because of their belief in God, but because of existence, security and identity. Since 1948, they have built a political, military and economic identity to be reckoned with. But that's only the beginning. Verse 27 continues: “And I will put my spirit within you, and cause you to walk in my statutes, and ye shall keep my judgments, and do them.” That is Israel's future, their national conversion. It will happen after the Church from among the Gentiles has been completed. Paul explains, “For I would not, brethren, that ye should be ignorant of this mystery, lest ye should be wise in your own conceits; that blindness in part is happened to Israel, until the fulness of the Gentiles be come in. And so all Israel shall be saved: as it is written, There shall come out of Sion the Deliverer, and shall turn away ungodliness from Jacob” (Romans 11:25-26).

What we are seeing now is the beginning of the fulfillment of Ezekiel 39:28: “Then shall they know that I am the LORD their God, which caused them to be led into captivity among the heathen: but I have gathered them unto their own land, and have left none of them any more there.” Not a single Jew will be left in any other country; they will all return to Israel.