The reason is as simple as it is amusing, "The Tales of Jacob Jacob" was one of the post popular works of 1600s English literature, and spawned four sequels "The Second Tale of Jacob Jacob", "Jacob Jacob and Jake Jacobson", "Jacob Jacob and the Jacobians", and lastly, "Bride of Jacob Jacob."

The Jacob Jacob series, sharing its name with the author Jacob Jacob, caused a large spike in the popularity of the name Jacob, as well as of the use of 'Jacob' as a "generic male name." Jacob was the 'average Joe' of the early 1700s, and, as Jacob Jacob himself put it "Jacob Jacob, jumping jacks, jacks jackson and takes jakes, for Jacob Jacob lacks Jack's jacks." The role that "Jacob Jacob" played in the development of British society is difficult to overstate.

Bibliography

Jacob Jacob, 1689, The Tales of Jacob Jacob

Jacob Jacob, 1691, The Second Tale of Jacob Jacob

Jacob Jacob, 1693, Jacob Jacob and Jake Jacobson

Jacob Jacob, 1694, Jacob Jacob and the Jacobians

Jacob Jacob, 1696, Bride of Jacob Jacob

Mattias Mattheson, 1970, Jacob Jacob and the English Revolution

William Williams, 1988, Jacob Jacob and the Development of British Popular Culture

Moto Moto et al, 2008, Madagascar: Escape 2 Africa

EDIT: APRIL FOOLS!