(TL;DR - Summary) Why study 2 first professional degrees in law? I know firsthand that a first degree in law from Canada, US, UK, or Oceania qualifies for postgraduate law programs (eg LLM) in these countries. So why did these 'legal eagles' NOT do an LLM, in place of the second LLB or JD? Doing a second LLB or JD, resembles repetition of material already learned.
(Optional Reading) I know that in North America, the LLB is superseded by the JD, but not in other Commonwealth countries (eg Oceania, UK). I exemplify with some notable legal practitioners:
SCOC Justices (whom I originally found from this article):
B.A. in 1926, an LL.B in 1928 (University of Alberta),
BA in 1930, a BCL in 1931 (Hertford College, Oxford University)
Gérard La Forest
BCL in 1949 (University of New Brunswick), BA in 1951, MA in 1956
(St John's College, Oxford)
Ian Binnie, LL.B in 1963, LL.M in 1988 (Cambridge University), LL.B in 1965 (U of Toronto)
I don't know what Justice Julien Chouinard studied at Oxford; so I don't list him.
Professor Trevor Farrow,
BA/MA Jurisprudence in 1992 (Wadham College, Oxford), LLB in 1993 (Dalhousie Law School)
Retired SCOTUS Justice David Souter,
A.B. magna cum laude in 1961 (Harvard),
MA Jurisprudence in 1963 (Magdalen College, Oxford), LLB in 1965 (Harvard Law School)