The reason is that Jews tend to delay marriage and childbirth at a rate higher than the general population, with a subsequent lowering of fertility rates. The new reproductive medical techniques have helped many infertile couples. Yet for many couples, adoption is the only alternative. Nonetheless, adoption does raise numerous halakhic as well as practical questions for Jews. There is a certain irony in the Jewish view of adoption.
Jewish sources teach two contradictory messages.
On one hand, the Bible and the Talmud are filled with wonderful examples of adoption and beautiful aggadic sayings about people who raise children born to others. On the other hand, because of the strong emphasis in Judaism on bloodlines and lineage, adoption as a formal legal procedure is totally unknown. In the Bible, Abraham adopts his servant Eliezer and Mordecai raises his orphaned cousin Esther. The Talmudic sage Abaye often quotes wise sayings in the name of his foster mother. Perhaps the most beautiful statement about adoption concerns Michal, the wife of King David.