It's just a coincidence.
Jacques is the French form of
James (ultimately from
Jacob), while Jack/Jock is short for
John (
Jean in French). Two completely different etymologies.
If you look at the IPA pronunciation, the names aren't even that similar: [jak] versus [djæk].
Alexandrina, Annabella, Clementine, Charlotte, Emilienne, Florence, Frederica, Katharina, Mary (May), Maud, Penelope, Rosamund, Theodora (Teddy).
Aubrey, Axel, Benedict, Bertrand (Bertie), Cuthbert, Dashiell, Everard, John (Jack) Leopold (Leo), Magnus, Matthias, Maximilian (Max), Wilfred.